We are in the process of moving from 2010 to 2013. There have been a couple VSTO add-ins for Office that used to work fine with 2010 but no longer work in 2013. Trying to enable them through the Add-ins menu does not work, and it says "Not loaded. A runtime error occurred during the loading of the COM add-in."

• Edited by diz17 16 hours 28 minutes ago

Hi,

This issue may be caused by the development environment changed, please see the below articles to troubleshoot this issue. 

Troubleshooting COM Add-In load failures

My Office Addin does not Load!

If you want to do further troubleshooting, such as debug code, I recommend you post the question to VSTO forum:

https://social.msdn.microsoft.com/Forums/vstudio/en-US/home?forum=vsto

The reason why we recommend posting appropriately is you will get the most qualified pool of respondents, and other partners who read the forums regularly can either share their knowledge or learn from your interaction with us. Thank you for your understanding.

George Zhao
TechNet Community Support