If you administer a busy database you will see this error from time to time. It is nothing to worry about, but it can be quite annoying when it stops you from doing something.

It simply means that session has a lock on an object that your session is trying to update (or lock). More specifically, your session has asked for a lock on the same object, but has specified the ‘nowait’ clause. The nowait clause, upon finding something locked, returns an error, rather than waiting for the lock to be released.

Your options are as follows:

• Make a cup of tea and try again later. Hopefully whatever was locking the object will have finished, and you can carry on.
• Attempt to find out who/what is locking the object and kill it off. Use this query to find the culprit.

References:

http://www.shutdownabort.com/dbaqueries/Performance_Locks_DML.php#Show-locked-objects