How old is the hard drive your media is stored on (although drives can fail at any time, it's been my experience that they fail right away or last for a while)? Yours might be starting to fail causing file corruption. Use Windows Explorer to schedule an error check when you reboot your computer. If the report scrolls off the screen faster than you can read it, no problem it is also placed in the Event Log. If you need help with either of these things, post back.
Try your failing album(s) again, after the fixes (if any) that the error check was able to do. If there are errors that could not be fixed, then the associated data may be lost. Try copying the 'bad' albums to a new folder (and start shopping for a new drive).
If the drive checked out ok and the album(s) still fail, try a "clean" reinstall of Winamp. This means removing all Winamp related files and settings from your computer. Some of this must be done manually. Search the forum for instructions or post back.
Win 7 Home Premium 64-bit SP1, WA Pro 22.214.171.12481 beta, cPro MPxi_remix skin, 5.1 speaker system