I'm wondering if you've hit the 4,000 differenct cell formats limit.
Check out...
http://support.microsoft.com/kb/213904

HTH,
--
Gary Brown

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"Brett" wrote:

I cannot edit the cell format in an excel worksheet. It is driving me nuts.
The sheet is not protected and I have tirned off the "locked" in the
protection tab under Cell Formatting.

I have tried copying to a new worksheet and the problem follows.....