Not all columns can be used for sorting, only indexed, simple columns can be used for sorting.
This article briefly describes how to check if a column is simple or not to determine if it can be used for sorting a report.
Note: This cannot be seen from the console (apart from that it is not available for sorting).
To see if a column is simple:
- Hover over the columns you selected for the report (within the Layout tab of the ReportProperties).
To check that it has been indexed make sure it has been flattened:
Check the value of the <IsFlat> tag for the column within the esmstg_meta.xml file (where 'esmstg' is the name of the database) in the database folder.
- If the tag value shows as True, the column has been flattened and is not indexed.