If you are looking to make changes to a report and see a 500 - Internal Server Error message when coming to save the report within the designer, this likely means the report is a standard report included with the software, even if this report was in the Other Reports ta and cannot be amended.
To make amendments to a report which is a standard report, you would first need to duplicate the report by following the below steps:
Click Reports then click Other Reports.
Expand the required folder then click the required report.
Click Duplicate button alongside the Design and Edit buttons and make changes to the duplicated version which will not be flagged as a standard report; therefore, changes are allowed.