I wasn't aware PP could import mp3 files. But I just tried it out. It failed on one & succeeded with the other. The one that failed had a long file title & was VBR. Whereas the other had a short filename & was CBR. Perhaps one of these areas is the reason you're having problems. Perhaps PP doesn't like files with long filenames or else, it can't import files encoded with VBR.

BTW the standard CBR bitrates are 320, 256, 224, 192, 160, 128, 96 kbps.

VBR of course being variable might be anything in between these.