The most likely cause of this problem is when some other CPAN process terminated in some unexpected way and didn't remove the lock file. Probably that was a one-time event. If so, there's no need to re-install perl, or CPAN.

Note that the lock file is just there to make sure you don't run two CPAN installer processes at the same time. If the lock is still there but there is no other CPAN process running it should be safe to remove it.

Try ps -eaf|grep 12651 to see if there is a CPAN process with that process id running. If there isn't, just answer Yes to the question (or remove the .lock file yourself before restarting CPAN).