The same has happened to me for quite a while. I made a half-hearted attempt
to get an answer from Microsoft tech support but they didn't seem to
acknowledge the problem. Some of my workbooks are fine, others have the
problem.

I wonder if the workbook where you've experienced the problem includes data
retrieved from an outside source.

Geoff

"wgnewman" wrote:

I making a workbook that will have approx. 130 charts and name each tab as I
go. Yesterday, I finished up number 68 and this morn I opened the workbook
and found that ALL the tabs have converted to numerals! What would cause
that? I depended on the tab names to inform me of alignment of data.