In software version 3.5.0 I’m seeing this error popup when loading a gerber for solder paste. The first time I tried, I received an error saying it couldn’t load the file. I tried again, and it loaded the Gerber, but when I loaded the drill file it gave me this error message. After retrying a few times, it then apparently succeeded at loading and calculating probing targets (no error popup) even though it was the same gerber and drill file each time.
FWIW, probably related to the bug in the probing system I mentioned a couple weeks ago (the phantom “zero height” error).