Whenever I try to log into Skype in Ubuntu 11.10 64-bit, it always says "Sign in failed" and "Another Skype instance may exist", thus preventing me from being able to log in.

I've had this kind of error in the past on previous Ubuntu releases where I would forget I already had Skype running and try opening it in the Dash again, and it was easily solved by just closing the extra window. But this time is different, and much more frustrating, because I get this error even after starting from a cold boot or running killall skype...times when AFAIK Skype should not even be running at all. Skype doesn't even show up in the Processes tab of System Monitor before I try starting it up, so I am pretty sure there is no second instance running.

I am using the 2.2.0.35-1 version of Skype from the Ubuntu Software Center. I have already tried reinstalling it to no avail. Any other suggestions?

Other things I've tried:

Tried the first answer to be posted to get the following output:

christopher@Xyz:~$ ps -ax | grep skype

Warning: bad ps syntax, perhaps a bogus '-'? See http://procps.sf.net/faq.html

10072 pts/0    S+     0:00 grep --color=auto skype

christopher@Xyz:~$ kill -kill 10072

bash: kill: (10072) - No such process

I have also tried a suggestion from the comment to this answer for a very similar problem (specifically, running pkill skype and pkill -9 skype), but that didn't work either.