Broken MSCOMRT2.OCX Caused Excel Add-in Exception

Last week I spent almost two days to resolve one issue. Excel add-in throw exceptions after an enterprise application update was installed. This happened initially in a product our team supports. The product is from a third party application suite by company C, where one Excel add-in is part of.

The symptom of the issue is that when Excel is opened, an exception is displayed right away. This one is caused by an add-in provided by the company C.



I contacted with the company which provides support the product. What they did was to remove monthview control from the add-in. It did not cause Excel error after that, however, I realized that this was not the right way to resolve the issue. The monthview is a common control from VB 6.0 control. Soon I found this control is MSCOMRT2.OCX, and there are some plains about its broken.

Soon I got calls from other department about the similar exceptions in Excel. They use different add-in and I realized that the root is to fix the control. After many discussions with other team member, I narrowed my focus on this control. I was right on this issue. I found a fix from Microsoft support knowledge base. The fix contains a cab file with only those two files:

mscomct2.inf
mscomct2.ocx

What I did was unregister the ocx file in %systemroot%/system32 first,



Then I copy those files to the path and register the ocx:



The fix seems very simple. However, at first no one knows the root of the issue. The update deployment team was afraid of the update would cause many user apps not working. I think the team work and web search played important role to get down the solution. Based on our communications on the issues and information we got, I finally found the right package as a fix.