ArcView returns this error when double-clicking an .apr file in Windows Explorer:
'Warning! The project (NAME) could not be opened.'
The APR file resides in a directory whose name has a space character. Double-clicking the APR file executes the arcview.exe file through DOS with the file path name as a parameter. DOS stops reading the file name once it encounters the space character; therefore it sends only part of the path name to ArcView.