I apologize for asking this as Mario recently answered it, but I can't find that message, or any of mine.
My motherboard went walkabout last month, so gradually that I failed to realize what was causing my cascade of problems. Solution: new computer - bigger, faster, more ram. BUT; I had to re-install everything, like IMatch. The database was on the boot drive that is no longer readable and the images are on the data drive D: that is just fine!
I used pack & go to recover the most recent back-up, and it put that db file in the IMatch folder on C: When I load that db, it looks for my images on C (not there).
Alas, the help file is unintelligible to me at this hour of the day and this year of my life.
Probably the best way to do this is using "relocate"; see also
https://www.photools.com/help/imatch/#file_management.htm#a_relocate
See Off-line Folders and Files (https://www.photools.com/help/imatch/#offline-files.htm), especially Files Moved to Another Disk or Computer (https://www.photools.com/help/imatch/#offline-files.htm?dl=h-6)