I am having a similar problem. When I try to collapse grades within a category, I am directed to a page with the error message "Error writing to database." When I click on the link for "More information about this error," I get this.
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This indicates that a general error occurred when Moodle tried to write to the database. If you turn on Debugging you will get more detailed information about what the problem is.
When importing questions in Aiken format after successful reading all questions this error emerges when saving in the database. No definite rule why. Ver. 2.0
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I cannot turn on debugging since I am faculty and not an an administrator, but when my admin tries collapsing columns in my gradebook, he can do it just fine.
Potential important information: 1) This problem is only in my 3 courses this semester and 1 course from last semester. In other past courses, I can expand and collapse columns normally. 2) My admin is on a PC, and I'm on a Mac.
Thanks in advance for any help.
-Derek..