An error occurred while loading or initializing an addin. Ask your administrator to check the Windows event log for more details. Dynamics will now close.

So you are trying to upgrade GP 2013 to GP 2013R2.

You launch GP and get the message as per subject.

When you check event viewer you get 'An exception occurred while trying to load or initialize the add in located at Excel Builder'


Reason for issue:
Your client gives you a mismatched database to GP folder.


To Resolve:
- Ensure the SLB from eone is installed
-Remove the excel related add ins from the Add In Folder in GP.
- Manually add the SLB module in the add remove of GP
-Launch GP. You will be fine.