CF will not disappear. Maybe your colour theme has changed.
Thank you graH-Guido for trying to help. But it seems that I did not state the problem clearly enough.
The problem is encountered by others using different worksheets. And I get the same error message using different worksheets.Slightly different issue then the one in the first message.
The file is somehow corrupted. One of the XML sections will have missing tags.
do you have an earlier backup of the file?