Fatal Error – Exception in mc3.dll / mc3d.dll

5 November 2015All, IT Services

Recently, we’ve begun to see this issue pop up more and more. We’ve seen it in AutoCAD based products.
While running the software you receive a dialog box titled, “Exception in mc3.dll / mc3d.dll ARX Command” and has an unhandled exception similar to, ”
Unhandled Exception C0000005 (Access Violation Reading 0x0000) at address F99260F4h”:

When you click the “OK” button you then receive a fatal error similar to, ”
FATAL ERROR: Unhandled Access Violation Reading 0x0000) Exception at F99260F4h:

The fix for this is as follow:

Navigate to Help > Desktop Analytics (or type in DesktopAnalytics at the command line)
Deselect the “Yes, I would like to contribute to this program” option:
Click OK.
Navigate to Help > Customer Involvement Program (or type in CustomerInvolvementProgram at the command line):
Select “No, I do not want to join the program at this time”:
Click OK.
Restart AutoCAD

Another option is to. . .

Close any/all open AutoCAD instances.
Browse to the following Windows registry key: HKEY_CURRENT_USER/software/Autodesk/MC3/ADAOptIn
Set the value to 0.
Launch the AutoCAD product and verify functionality has been restored.

To be on the safe side, back up the Windows registry prior to making any manual edits to it (like the one in the above steps).
This last option comes directly from the Autodesk Forum and can be found here: AutoCAD 2016 mc3.dll / mc3d.dllARX Command Error