It appears that Ruby 1.9 isn't happy with the "Run Script" (command-R) in the ShellScript.tmbundle included with TextMate Version 1.5.7 (1436). Or, that if you have the recent Ruby.tmbundle checked out from SVN, you'll need the ShellScript.tmbundle as well.
I got:
(erb):30:in `concat': character encoding differ (ArgumentError) from (erb):30:in `html_head' from /usr/local/lib/ruby/1.9.0/erb.rb:743:in `eval' from /usr/local/lib/ruby/1.9.0/erb.rb:743:in `result' from /Library/Application Support/TextMate/Support/lib/web_preview.rb:117:in `html_head'
When I ran shell scripts from TextMate in Ruby 1.9. This stems from the left and right single quotation marks used in the Textmate 1.5.7 command to frame the window title: ‘Run <filename.sh>’
The issue is already fixed in the SVN, so simply checking out the newest version of ShellScript.tmbundle seems to fix the problem.
Best, Charles