My ringtones go blank, but i access the text message again and they're fine?

Ok, I've got an old motorola phone from alltel (model v262 i believe). It doesn't have a camera, but it's a a flip phone and has a color screen. I converted an mp3 file into a .wav file then used qcp converter to convert it to a ringtone. I had to add .mid to the end for it to work. I then used axcessmypics.com to send it to my phone. I got the text message with the ringtone and selected to save and set as ringtone. It plays fine and works fine. But after a while (maybe a day or two?) the file's contents pretty much disappear. When I get a call, the ringtone is just quiet static. I went to play the ringtone manually, and it's still quiet static. So, I went back to the text message and saved the song again. It works for some time, then goes corrupt or whatever again. So this time I tried saving it without setting it as a ringtone, then setting it as a ringtone. Any ideas on what to do if it happens again? I missed a call earlier today because of it.