If you have recently found this error pops up while opening or working in ACAD or ACAD related products this hotfix could help resolve this issue.

Issue:

When opening the program, a file or while working in AutoCAD, the program crashes with an unhandled exception error in the mc3.dll or mc3d.dll files, such as the following: 
 
Exception in mc3.dll / mc3d.dll ARX Command
Unhandled Exception C0000005 (Access Violation Reading 0x0000) at address B91B60F4h 

Causes:

Damaged WHITELIST.XML file, specifically affecting AutoCAD Architecture 2016 and AutoCAD MEP 2016.

Solution:

To fix the crash for AutoCAD MEP 2016 and AutoCAD Architecture 2016:

Exit all Autodesk programs.

Navigate to the following folder:

For AutoCAD Architecture 2016:

C:\Users\<user>\AppData\Roaming\Autodesk\ARCHDESK\2016\{5783F2D7-F004-0409-2102- 0060B0CE6BBA}\7.8.44.0\MC3

For AutoCAD MEP 2016:

C:\Users\<user>\AppData\Roaming\Autodesk\BLDSYS\2016\{5783F2D7-F006-0409-2102-0060B0CE6BBA}\7.8.44.0\MC3

Delete the file WHITELIST.XML.

Note: The numbered build folder containing the XML file (the folder just before MC3) varies, based on whether or not any service packs are installed. If the XML file does not appear in the build folders listed above, check the other numbered build folders for the XML file.

Restart the computer.

Launching AutoCAD Architecture 2016 or AutoCAD MEP 2016 will download a corrected WHITELIST.XML file, as long asDesktop Analytics is enabled.

For other versions of AutoCAD including AutoCAD LT: 
Bypass the functionality that causes the crash by doing the following:

Go to Help > Desktop Analytics (or type DESKTOPANALYTICS on the command line).
Deselect the “Yes, I would like to contribute to this program.” option.
Click OK.

Next:

Go to Help > Customer Involvement Program (or type CUSTOMERINVOLVEMENTPROGRAM on the command line).
Select “No, I do not want to join the program at this time.”
Click OK.
Restart the program.

If AutoCAD crashes before you can disable the Desktop Analytics and CIP options, you can make an edit in the registry:

Close all instances of AutoCAD.
Press WINDOWS-R on the keyboard to bring up the Run window, enter REGEDIT and click OK.
Navigate to and select the following registry folder:
HKEY_CURRENT_USER/software/Autodesk/MC3
On the right pane of the window, double-click ADAOptIn.
Change the value to 0 (zero).
Click OK and close the Registry Editor.

Alternatively, if you have an older version of AutoCAD installed, disabling the Desktop Analytics and CIP options within it should apply to version 2016 too. 

Warning by Autodesk!
Problems caused by improperly editing the Windows registry could render your computer operating system unusable. Microsoft provides a wealth of critical information that you need to know about the registry in the Microsoft Knowledge Base. Use the Microsoft Registry Editor only at your own risk and only after backing up the registry as outlined for your operating system in the Microsoft article How to back up and restore the registry in Windows and in the related solution How to backup the system registry. Additional information about the registry is also contained in the Help topics in the Microsoft Registry Editor.

 

Link directly to Autodesk website about this issue and fix.