Opening a Visual Basic project file that uses the ArcObjects Map control returns:
Error during load. Refer to VB project name.log for details.
After dismissing this error message, the log file that gets created contains the following information:
Class esriControlsCtl.MapControl of control MapControl1 was not a loaded control class.
The Visual Basic project was saved with the ArcGIS 8.1 prerelease version of the Map control. The signature of the Map control has changed since the prerelease version.