Hello Ian,

In versions of Excel prior to version 12 (2007), the total number of unique cell styles in a workbook (combinations of all cell formatting) is 4,000. Excel 2007 has a limit of 64,000 formats. You will need to review your layout, and find ways to consolidate your formatting. For example using a summary sheet for data, rather than formatting each sheet the same, move the data to the proper position on the summary sheet instead.

Sincerely,
Leith Ross