It sounds like you may be experiencing a problem with Excel's calculation settings. Here are a few steps you can try to resolve the issue:

1. Check your calculation settings: Go to the "Tools" menu, select "Options", then click on the "Calculation" tab. Make sure that "Automatic" is selected under "Calculation options". If it is set to "Manual", Excel will not recalculate formulas automatically, which could be causing the issue you're experiencing.
   
2. Check for circular references: If your formula refers to the cell it is in, or if there is a chain of formulas that refer to each other, Excel may not be able to evaluate the formula. Check for circular references by going to the "Tools" menu, selecting "Options", then clicking on the "Calculation" tab. Make sure that "Iterative calculation" is not selected.
   
3. Check for hidden characters: Sometimes, hidden characters can cause problems with formulas. Try copying the formula into a text editor (like Notepad) and then copying it back into Excel. This can help remove any hidden characters that may be causing the issue.
   
4. Try using a different formula: If none of the above steps work, try using a different formula to achieve the same result. For example, you could try using the SUMPRODUCT function instead of COUNTIF.

I hope these suggestions help you resolve the issue you're experiencing with your formula.