Originally Posted by DxTer
I did run the command using sudo and also restarted my system quite a bit time so I guess there are no other packages of synaptic or software center running? right?
If you haven't opened anything, then the command above should work just fine. Occasionally it'll fail because the update daemon will be using apt to check for updates, but that usually only takes a minute or two, so if it's still saying no, then try waiting 5 minutes and try again. If it still refuses to co-operate, and since you've rebooted, it should be safe to remove the lock files. I got that idea from this mailing list thread here.