If you create an "application" with just this single line of code:
and hit "Launch", JS compiler will stop with the error, but the "Launch" button will remain disabled, and the only way to work with the application again will be to switch to some other application in Titanium Developer and then back to the application in question.
I think that after any fatal compilation error the "Launch" button should be re-enabled.
I've seen that too and agree, it should be re-enabling itself. Sometimes clicking Stop will help (even if the app isn't actually running in the simulator). If not, switching to the Edit tab, then back to Test & Package should do it.
Another way to clean up a build is to open Terminal, go to [app directory]/build/iphone and execute this command:
xcodebuild clean -configuration Debug
You really shouldn't have to do that very often, but sometimes for piece of mind I'll try it if something's no quite working right and I want to rule that out.
you can delete the Apps folder, this will force a full Xcode compile.
Go to you project folder and find the folder /build/iphone/build/
Delete all content in this last folder.