Cannot update Stage-Probability Mapping

Cannot update Stage-Probability Mapping

Hi, I am a ZOHO CRM user for free and evaluating this system.

I'm trying to update Stage-Probability Mapping now.
At first I can update, but I cannot now. I don't know what was happen.

For example, when I edited a stage name from "Realize"  to "Realize1" (just adding "1") and push the "Save" button;

I received an error message "Error occured while updating Stage-Probability Mapping."

The mapping table was not updated.

I tried to log-out and log-in again, but the problem was not solved.
I think that I am a free user but it is not a cause of this problem.

How can I update the mapping table?