This question already has an answer here:
I'm trying to update from 10.10. This has become a problem for me. After typing
I get the following screen.
Thereafter I try to update the usual way and get this pair of messages: and
After the last message, the update process automatically closes.
Can somebody help me either by pointing out what's preventing me from upgrading or how not to update to 11.04 but to 12.04 or 12.10 directly?