first post the code here for us to see so that we can understand what you wanna do

then

find line 79 and check if you've made a silly mistake (VERY easy to do with MEL). It sounds like you're trying to rename an object to a name which already exists. Normally maya handles this by adding an incremental number on the end... hmmm post the code or the offending portion and I'll take a look for ya

Alan