Correlate - error if there is a period in a folder name in the path.
e.g. c:\pass\Adv. Raster\class1\test.rgf
The "." in Adv. Raster causes the problem. It's not a common way of making folder names, but it does cause a mysterious, hard to troubleshoot, bug for the user.
I think, internally, the period short-circuits the parsing of the rgf filename & gives an error that it can't find the rgf.