So in my case the problem is probably the Ü in my name, thanks for the hint

hello.
i have the same problem on a freshly installed sup (via aur on arch linux)
i've just run the sup-config tool, no other modifications.
seems to be caused by the 'é' sign in my name in the From:, doesn't crash if i 
replace it with a normal 'e'

--- Encoding::CompatibilityError from thread: main
incompatible encoding regexp match (ASCII-8BIT regexp with UTF-8 string)
/usr/lib/ruby/gems/1.9.1/gems/sup-0.10.2/lib/sup/modes/edit-message-
mode.rb:205:in `match'
/usr/lib/ruby/gems/1.9.1/gems/sup-0.10.2/lib/sup/modes/edit-message-
mode.rb:205:in `match'
/usr/lib/ruby/gems/1.9.1/gems/sup-0.10.2/lib/sup/modes/edit-message-
mode.rb:205:in `mime_encode_address'
/usr/lib/ruby/gems/1.9.1/gems/sup-0.10.2/lib/sup/modes/edit-message-
mode.rb:374:in `block in build_message'
/usr/lib/ruby/gems/1.9.1/gems/sup-0.10.2/lib/sup/modes/edit-message-
mode.rb:369:in `each'
/usr/lib/ruby/gems/1.9.1/gems/sup-0.10.2/lib/sup/modes/edit-message-
mode.rb:369:in `build_message'
/usr/lib/ruby/gems/1.9.1/gems/sup-0.10.2/lib/sup/modes/edit-message-
mode.rb:322:in `send_message'
/usr/lib/ruby/gems/1.9.1/gems/sup-0.10.2/lib/sup/mode.rb:51:in `handle_input'
/usr/lib/ruby/gems/1.9.1/gems/sup-0.10.2/lib/sup/buffer.rb:270:in `handle_input'
/usr/lib/ruby/gems/1.9.1/gems/sup-0.10.2/bin/sup:270:in `<module:Redwood>'
/usr/lib/ruby/gems/1.9.1/gems/sup-0.10.2/bin/sup:64:in `<top (required)>'
/usr/bin/sup:19:in `load'
/usr/bin/sup:19:in `<main>'

thanks!

Have you tried to put all your hooks aside and try without them?

Well, I still have it with new messages, and it starts to really get on my 
nerves...
It seems to work when replying but with new messages it just crashes when I try 
to send them.

Sorry, forgot the exception log.
Regards,
Philipp

Now someone told me a workaround that seems to work for newly composed messages, 
but I get the same issue when attempting to open certain threads:

$ sup
which: no gpg in 
(/bin:/usr/bin:/sbin:/usr/sbin:/opt/kde/bin:/usr/bin/perlbin/site:/usr/bin/perlb
in/vendor:/usr/bin/perlbin/core:/opt/qt/bin)
[2010-02-05 02:05:40 +0100] ERROR: oh crap, an exception
----------------------------------------------------------------
I'm very sorry. It seems that an error occurred in Sup. Please
accept my sincere apologies. Please submit the contents of
/home/murks/.sup/exception-log.txt and a brief report of the
circumstances to http://masanjin.net/sup-bugs/ so that I might
address this problem. Thank you!

Sincerely,
William
----------------------------------------------------------------
--- Encoding::CompatibilityError from thread: load messages for thread-view-mode
incompatible character encodings: UTF-8 and ASCII-8BIT
/usr/lib/ruby/gems/1.9.1/gems/sup-0.10.1/lib/sup/modes/thread-view-
mode.rb:726:in `message_patina_lines'
/usr/lib/ruby/gems/1.9.1/gems/sup-0.10.1/lib/sup/modes/thread-view-
mode.rb:787:in `chunk_to_lines'
/usr/lib/ruby/gems/1.9.1/gems/sup-0.10.1/lib/sup/modes/thread-view-
mode.rb:658:in `block in regen_text'
/usr/lib/ruby/gems/1.9.1/gems/sup-0.10.1/lib/sup/thread.rb:81:in `block (2 
levels) in each'
/usr/lib/ruby/gems/1.9.1/gems/sup-0.10.1/lib/sup/thread.rb:170:in `block (2 
levels) in each_with_stuff'
/usr/lib/ruby/gems/1.9.1/gems/sup-0.10.1/lib/sup/thread.rb:170:in `block (2 
levels) in each_with_stuff'
/usr/lib/ruby/gems/1.9.1/gems/sup-0.10.1/lib/sup/thread.rb:170:in `block (2 
levels) in each_with_stuff'
/usr/lib/ruby/gems/1.9.1/gems/sup-0.10.1/lib/sup/thread.rb:170:in `block (2 
levels) in each_with_stuff'
/usr/lib/ruby/gems/1.9.1/gems/sup-0.10.1/lib/sup/thread.rb:170:in `block (2 
levels) in each_with_stuff'
/usr/lib/ruby/gems/1.9.1/gems/sup-0.10.1/lib/sup/thread.rb:170:in `block (2 
levels) in each_with_stuff'
/usr/lib/ruby/gems/1.9.1/gems/sup-0.10.1/lib/sup/thread.rb:170:in `block (2 
levels) in each_with_stuff'
/usr/lib/ruby/gems/1.9.1/gems/sup-0.10.1/lib/sup/thread.rb:168:in 
`each_with_stuff'
/usr/lib/ruby/gems/1.9.1/gems/sup-0.10.1/lib/sup/thread.rb:170:in `block in 
each_with_stuff'
/usr/lib/ruby/gems/1.9.1/gems/sup-0.10.1/lib/sup/thread.rb:169:in `each'
/usr/lib/ruby/gems/1.9.1/gems/sup-0.10.1/lib/sup/thread.rb:169:in 
`each_with_stuff'
/usr/lib/ruby/gems/1.9.1/gems/sup-0.10.1/lib/sup/thread.rb:170:in `block in 
each_with_stuff'
/usr/lib/ruby/gems/1.9.1/gems/sup-0.10.1/lib/sup/thread.rb:169:in `each'
/usr/lib/ruby/gems/1.9.1/gems/sup-0.10.1/lib/sup/thread.rb:169:in 
`each_with_stuff'
/usr/lib/ruby/gems/1.9.1/gems/sup-0.10.1/lib/sup/thread.rb:170:in `block in 
each_with_stuff'
/usr/lib/ruby/gems/1.9.1/gems/sup-0.10.1/lib/sup/thread.rb:169:in `each'
/usr/lib/ruby/gems/1.9.1/gems/sup-0.10.1/lib/sup/thread.rb:169:in 
`each_with_stuff'
/usr/lib/ruby/gems/1.9.1/gems/sup-0.10.1/lib/sup/thread.rb:170:in `block in 
each_with_stuff'
/usr/lib/ruby/gems/1.9.1/gems/sup-0.10.1/lib/sup/thread.rb:169:in `each'
/usr/lib/ruby/gems/1.9.1/gems/sup-0.10.1/lib/sup/thread.rb:169:in 
`each_with_stuff'
/usr/lib/ruby/gems/1.9.1/gems/sup-0.10.1/lib/sup/thread.rb:170:in `block in 
each_with_stuff'
/usr/lib/ruby/gems/1.9.1/gems/sup-0.10.1/lib/sup/thread.rb:169:in `each'
/usr/lib/ruby/gems/1.9.1/gems/sup-0.10.1/lib/sup/thread.rb:169:in 
`each_with_stuff'
/usr/lib/ruby/gems/1.9.1/gems/sup-0.10.1/lib/sup/thread.rb:170:in `block in 
each_with_stuff'
/usr/lib/ruby/gems/1.9.1/gems/sup-0.10.1/lib/sup/thread.rb:169:in `each'
/usr/lib/ruby/gems/1.9.1/gems/sup-0.10.1/lib/sup/thread.rb:169:in 
`each_with_stuff'
/usr/lib/ruby/gems/1.9.1/gems/sup-0.10.1/lib/sup/thread.rb:170:in `block in 
each_with_stuff'
/usr/lib/ruby/gems/1.9.1/gems/sup-0.10.1/lib/sup/thread.rb:169:in `each'
/usr/lib/ruby/gems/1.9.1/gems/sup-0.10.1/lib/sup/thread.rb:169:in 
`each_with_stuff'
/usr/lib/ruby/gems/1.9.1/gems/sup-0.10.1/lib/sup/thread.rb:78:in `block in each'
/usr/lib/ruby/gems/1.9.1/gems/sup-0.10.1/lib/sup/thread.rb:75:in `each'
/usr/lib/ruby/gems/1.9.1/gems/sup-0.10.1/lib/sup/thread.rb:75:in `each'
/usr/lib/ruby/gems/1.9.1/gems/sup-0.10.1/lib/sup/modes/thread-view-
mode.rb:647:in `regen_text'
/usr/lib/ruby/gems/1.9.1/gems/sup-0.10.1/lib/sup/modes/thread-view-
mode.rb:162:in `buffer='
/usr/lib/ruby/gems/1.9.1/gems/sup-0.10.1/lib/sup/buffer.rb:380:in `spawn'
/usr/lib/ruby/gems/1.9.1/gems/sup-0.10.1/lib/sup/util.rb:553:in `method_missing'
/usr/lib/ruby/gems/1.9.1/gems/sup-0.10.1/lib/sup/modes/thread-index-
mode.rb:112:in `block in select'
/usr/lib/ruby/gems/1.9.1/gems/sup-0.10.1/lib/sup.rb:77:in `block in 
reporting_thread'

It seems that when I compose a new message and try to send it sup crashes with 
this error. I had it on two ocassions today. I don't even remember what the 
first mail was about, the information is simply lost. The second case is 
reproducable. Replying seems to work fine.

$ sup
which: no gpg in 
(/bin:/usr/bin:/sbin:/usr/sbin:/opt/kde/bin:/usr/bin/perlbin/site:/usr/bin/perlb
in/vendor:/usr/bin/perlbin/core:/opt/qt/bin)
[2010-02-02 22:53:10 +0100] ERROR: oh crap, an exception
----------------------------------------------------------------
I'm very sorry. It seems that an error occurred in Sup. Please
accept my sincere apologies. Please submit the contents of
/home/murks/.sup/exception-log.txt and a brief report of the
circumstances to http://masanjin.net/sup-bugs/ so that I might
address this problem. Thank you!

Sincerely,
William
----------------------------------------------------------------
--- Encoding::CompatibilityError from thread: main
incompatible encoding regexp match (ASCII-8BIT regexp with UTF-8 string)
/usr/lib/ruby/gems/1.9.1/gems/sup-0.10.1/lib/sup/modes/edit-message-
mode.rb:205:in `match'
/usr/lib/ruby/gems/1.9.1/gems/sup-0.10.1/lib/sup/modes/edit-message-
mode.rb:205:in `match'
/usr/lib/ruby/gems/1.9.1/gems/sup-0.10.1/lib/sup/modes/edit-message-
mode.rb:205:in `mime_encode_address'
/usr/lib/ruby/gems/1.9.1/gems/sup-0.10.1/lib/sup/modes/edit-message-
mode.rb:374:in `block in build_message'
/usr/lib/ruby/gems/1.9.1/gems/sup-0.10.1/lib/sup/modes/edit-message-
mode.rb:369:in `each'
/usr/lib/ruby/gems/1.9.1/gems/sup-0.10.1/lib/sup/modes/edit-message-
mode.rb:369:in `build_message'
/usr/lib/ruby/gems/1.9.1/gems/sup-0.10.1/lib/sup/modes/edit-message-
mode.rb:322:in `send_message'
/usr/lib/ruby/gems/1.9.1/gems/sup-0.10.1/lib/sup/mode.rb:51:in `handle_input'
/usr/lib/ruby/gems/1.9.1/gems/sup-0.10.1/lib/sup/buffer.rb:270:in `handle_input'
/usr/lib/ruby/gems/1.9.1/gems/sup-0.10.1/bin/sup:270:in `<module:Redwood>'
/usr/lib/ruby/gems/1.9.1/gems/sup-0.10.1/bin/sup:64:in `<top (required)>'
/usr/bin/sup:19:in `load'
/usr/bin/sup:19:in `<main>'