This didn't help me. I don't have RM4 installed on the same computer as RM3. I'm getting the same error message that Bill got. I exported gedcom file from RM3 to a flash drive. Then I moved the gedcom file from the flash drive to a subfolder called roots magic that I created in the documents folder. I tried the same thing with a RM3 database file I copied. Neither one works. It's very frustrating. My RM3 is on a windows XP OS, the RM4 is on a Windows 7 starter OS on a netbook.
Okay, I just figured out what I did wrong. I didn't understand at first that I was supposed to use the same subfolder that I put the ged file in to create the new database in. Once I changed that from the default program file folder then it worked.