While working with a client recently they had an issue where all the toolbar icons wouldn’t show, and doing any operations inside Acrobat results in a generic “An internal error has occurred” message.

A colleague tried to do a repair and then re-install to no avail.

I found the fix was the go into the %localappdata% and %appdata% locations.
Go into the Adobe folder.
Find the Acrobat folder and renamed it to Acrobat.old
I try to keep those around in case they need to be referenced later.

After the Adobe Acrobat worked without further issue.

I suspect the cache or preferences became damaged.