This error appear when your try to format a cell or a range of cells.
And the reason you getting this message because your workbook exceeds more than approximately 4,000 different combination of cell format. A combination is defined as a unique set of formatting elements that are applied to a cell. A combination includes all font formatting (for example: typeface, font size, italic, bold, and underline), borders (for example: location, weight, and color), cell patterns, number formatting, alignment, and cell protection.
If you are in the middle of saving your files, just save as the file to a different name. So, it didn't temper the previous version of your file.
For the quick fix:
1. Use the same type of font or use the standard font
2. Use borders format consistently. For example do not overlap formatting the same border
3. Remove the patterns by clicking No Color in the Patterns tab of the Format Cells dialog box
Try to save your file after apply these quick fixes.
Some ways to solve this problem:
1. Install or use Open Office. Open the file. Save and replace the file.
Open Office organized and formatting information is slightly different from Microsoft. Hopefully can solve the issue temporarily.
2. This final tip WILL works 100%. Upgrade your current Excel version to Excel 2007. Because the limitation is upgrade to 64.000 different combination.
Hopefully this tip can help. Just drop some other comments that can resolve the issue.