CAD tip # 8890:

This is caused by wrong setting of the open mechanism for the particular file type - in the Registry. Start REGEDIT and go to the branch:

HKEY_CLASSES_ROOT\Inventor.PartDocument/SHELL/open

There you will find two keys: command and ddeexec

The command key should be set to the Inventor executable path - e.g.: C:\Program Files\Autodesk\Inventor 2012\Inventor 2012\bin\inventor.exe /dde (short folder names can be used)

The ddeexec key is more important - it should be set to the string: [open("%1")]

After you change the settings, restart Inventor.

If you can see other subfolders in the SHELL tree - e.g. a GUID-type subfolders (starting with e.g. "{0001...") and the above mentioned procedure has not helped, try to remove these subfolders - first make a backup of your Registry contents.