There are two possible causes to this alert:
Cause #1:
If you have changed the name of a Claris application to have a period in front of it (for example ".MacWrite Pro"), the application will give you an erroneous error message that it has been modified and is not usable, or that the File in Busy, and to try again later. This only occurs on machines running System 6.
This is a well-known "feature" of all systems before System 7. Filenames starting with a period are supposed to be reserved for drivers (such as .Sony).
The solution is to remove the period from the front of the name.
Cause #2:
AutoDoubler is running, and has compressed the file before you have entered your name and serial number into the opening screen. The solution is to uncompress the file, run the application, personalize the app. with your name, etc. You can then let AutoDoubler compress the program, and it should work correctly.