Which Mac OS are you using? And what type of icon do these mp3's have? Also, which mp3 players do you have? Do they play in iTunes?
I haven't come across that problem unless they were a pc format that Toast didn't understand. If you have MP Rage you can change their file properties to say that of iTunes by changing the creator of the file. Also Audion has some mp3 codecs that iTunes doesn't have. I had a 3hr concert mp3 I dwnlded yesterday but Audion was the only one that could play it. I used Audion to convert it to AIFF.
Oh & iTunes refused to import/play the concert & Toast also refused. Yours could be the same format I had, but then nowadays there's so many variations of them they might be something else again. You are aware there's multiple types of mp3's requiring different codecs to play them don't you? Each mac mp3 player can play a no. but not always all. As I said, for the difficult ones I've found Audion to do the job.