Yes, as Memnoch said.. Personally I have had this happen after I uninstalled BG2 and then re-installed, but it isn't nothing what some little registry cleaning cannot fix
The CD5 thingie comes from those bonus or whatever merchants I think..
If you are familiar on how to clear the registry, you can just uninstall it, clear the registry of all the mess related to Baldur's Gate, Bioware, Black Isle, Interplay and then re-install it. Does the trick for me every time.