Comment 9 for bug 146864

On Gutsy, I've just replicated the symptoms using the (mis-typed) command "sud su" - obviously sud was meant to be sudo. :)

The CLI had a think about it, I realised my mistake & hit CTRL+C to receive:

KABOOOM!!!

Whoops, command-not-found has crashed! Please file a bug report at:
https://bugs.launchpad.net/ubuntu/+source/command-not-found
Please include the following information with the report:
No module named CommandNotFound
Traceback (most recent call last):
  File "/usr/lib/command-not-found", line 10, in <module>
    from CommandNotFound import CommandNotFound
ImportError: No module named CommandNotFound
Python version: 2.5.1 final 0

This can be reproduced at will if you leave a short moment before hitting CTRL+C after Return... It is often accompanied by the pre-symptom:

'import site' failed; use -v for traceback

Note that if you do have problems replicating, try adding a heavy CPU load to your machine & then issue.