I'm sorry, but I'm unable to replicate this "checking discs" operation when I do a test to burn MP3's from hard drive to audio CD (CDDA). When I do this operation with Nero it immediately goes into converting the MP3 files to audio and burning the selections without any "checking discs" message.
There must be something about your particular setup or settings that is causing this message and error. I haven't heard of it before.
One possibility is that perhaps the MP3 files are corrupted or don't meet the standard that Nero requires for successful MP3 conversion to audio CD. This is even more likely if you got the MP3 files from the internet. Try creating some MP3 files yourself and use them for a test to see if you can successfully burn them to an audio CD-R. If this works, then you can assume that the other MP3 files have some type of defect that is causing Nero to freeze. Even if the MP3 files have problems, Nero shouldn't freeze, so this isn't a very satisfactory theory.