Songs greyed out on my iPod.

I've had this problem for a couple of years, or so. When I add songs to my 2nd generation iPod Touch selected tracks "greyed out" and not playable. I thought it was an issue of the bit rate being too high. Although I encoded at lower rates and eventually got them to load I don't think bit rate is the issue. I've looked at various solutions online and they don't apply to me. I've always had my itunes set to be managed manually. One solution had me emptying the purchases folder in the Raw file system on my ipod, but that was already empty. I'm reluctant to fully restore, because having used different computers over the years, most of the songs on my ipod are no longer on my computer and would be difficult to replace. Any ideas?