It's likely that your tags are stored in Unicode but whatever program you are using can only read tags stored in ASCII. MP3tag can fix the problem. See the following sticky forum topic:
Problems with ID3v2 tags in Unicode format?, Tags not (correctly) read by other programs?
It worked for me. I am using Windows Media Player 9 - the latest is WMP 11 - and I was getting "C00D1199: Cannot play the file" errors. I cannot upgrade to a later version of WMP because I'm using it at work and nagging the IT department for entertainment purposes is, needless to say, frowned upon. As it stands, I'm the only person in the whole office, other than perhaps the on-site IT person, who has WMP version 9 or better or Firefox.