If you have programs on your computer that loaded different versions of a .dll file it can do this when some of those programs are opened and the other version is loaded into memory.

I am not familiar with XP, but under the older operating systems under system tools, system information there is/was a conflict manager where you could check to see if you have conflicting files. If you do, you need to eliminate the older .dll and keep the newest one (the one with the largest number). Example version 4.223 and version 4.333 (you would keep the 4.333).

Most are backwards compatible with prior versions.