Error: "Drawing file is not valid" when opening a file in AutoCAD

While opening a drawing file in AutoCAD, the following error message appears: 
 

AutoCAD Message 
Drawing file is not valid. 

 

Causes:

The error message usually indicates that the drawing has been damaged beyond use, but there could be other environmental factors causing it to fail or to become corrupted.

Solution:

• If the drawing was last saved in a newer version of AutoCAD, resave it from that version to an older file format, one that is compatible or older than the version of AutoCAD being used.
• Try opening the drawing file directly instead of using the Recent Documents menu.
• If the file was created in a non-AutoCAD product, try opening the file in the native product and exporting to 'AutoCAD DWG' format, if available. 
• Check that the storage location that holds the drawing is working properly.
• Move the drawing to a different location--ideally to the local hard disk, to rule out network or cloud storage issues.
• If the drawing was emailed, have the sender ZIP the file and resend it.
• Attempt to clean and repair the file