An error -1 is an error that the program couldn't identify the nature of. Sometimes it's just a network connection error. You can try, in this order:
1. Try again to close/open the program on that station. Try #2 if this doesn’t work.
2. Reboot the workstation where this error is occurring, and then try to open the program. Try #3 if this doesn’t work.
3. Reboot the server on which the data is located, and then try to open the program (try opening it at the server first if you have the program files installed there. If that succeeds, try again on the workstation. Try # 4 if this doesn’t work.
4. See if any other workstations are having the same problem. If they aren't, it's likely a network connection problem at the workstation that is. If they are, it could be a system-wide network connection problem or a corrupt forms.dbf file.