Hi again
The only thing that occurs to me is that maybe the set was missing a sample and when Live tried to find the missing sample itself it thought something with "strings" in the file name must be right, and it has associated that clip with this file.
While your set may still open ok, maybe you have a missing sample in one of your clips somewhere... Either take a look round for a clip that uses a sample with a similar name to the pop-up error file name, or you can do it by trial and error and make copies of your set using "save as..." and removing suspect tracks each time until you isolate which track contains the bad clip...
Hope that helps...