When a SAP BW data connection is used, adding a variable to a sheet title produces the error "Internal Error - An unexpected error occurred and the operation could not be completed" and dynamic field headers no longer work.
840413
With a table calc an reference line in the view, nested sorting failed with a "No such column" error.
841863
When using a filter, sorting on a MSAS dimension resulted in an "Internal error - An unexpected error occurred and the operation could not be completed" message.