I recently had this problem with Toucan on Windows XP SP2, only when trying to encrypt a file using Rijndael. The 'Abort' button in the progress form wouldn't respond, and the only way to get rid of it would be killing the ccrypt process through the task manager.
I ran ccrypt from the command line in verbose mode, and got a prompt that said something similar to this:
'The file is write-protected, do you want to process it anyway?[y/n]_'
The underlying problem was a file permissions one, but it seems that Toucan calls ccrypt.exe (shellexecute?), and when ccrypt asks for some user's input apart from the initial command line arguments, Toucan just sits there waiting for the process to return.
I also noticed that the progress form also stalls if you try to encrypt a file with Rijndael without providing a password.
Congratulations for the great application.