This has been a problems for a few years. When LW has been on for a while, iTunes seems to drop off or become unreliable importing. Best answer is to close LW & re-open when this starts happening. Else, don't auto-import to iTunes. Instead add them manually. This is what i do now so I can be sure the songs have been added to iTunes.

LW may confuse same title file as being the same when it's actually different size or attributes. That's whey the LW error message. I personally use auto Append filename when two files are of same name, then check them later before adding to iTunes to see if they are same file or not. Takes time though. To add that option, go to LW prefs > Saving > Advanced > Always Append (#) to the filename.

iTunes will add files of same name on condition they are different. ie: different file composition different size, etc.