There has been a long standing out of memory bug when attempting to import mp3's into Sonar that was fixed in X3d. I do a lot of backing tracks for my cover band in Sonar and fixing that bug has made my life a whole lot easier.
My normal workflow is to import the original audio track, transcribe the parts, find or create the sounds, produce the mix, then bounce it with a click track for our live shows. I used to have to burn my mp3's to CD's, rip them to wav's, then import them into Sonar. Now I can import the mp3's directly into Sonar, this makes getting the reference track into my workspace much easier and I don't have to make CD's that I use once and throw away.
Thanks!

Actually I think the bug was only importing MP3's with certain kinds of tags. Have you actually managed to import the same MP3 files that triggered the error message in the past?

I remember it was quite a few years ago where this was discussed. Noël talked about the problems associated with decoding mp3s that had particular tags which had been written by the program that authored those particular files. So it ended up that Sonar couldn't read some mp3 depending on the tags in the file.

Yes this was fixed in X3D. We now use Media Foundation to decode MP3's with imbedded art and tags that previously failed to load. 
MF allows us to load several formats that were not natively supported earlier including MP4 AAC etc. 

slartabartfast
Actually I think the bug was only importing MP3's with certain kinds of tags. Have you actually managed to import the same MP3 files that triggered the error message in the past?

Yes, nothing I got from Amazon would import. Now it works fine.