Fix for Editor Error: An Exception has been encountered. This may be caused by an extension.

Are you seeing this error message in MET/CAL Editor?  

Here is the solution for that error.

Go to your C drive\Users and find your user name (computer user name) :  (This is what I see when I am logged in to my computer).  You will substitute your user name.  

Look for these two folders:
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remove the mce32 folder from "Local":

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Do the same thing in the "Roaming" directory 

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Restart MET/CAL Editor.