When manually trying to rebuild an AD index, you see the error “Exact data profile "xxx" is already being indexed”.
Release : 15.8
Even though you see a RSOD when its generating the index, the index itself is still being generated fine. If you look at the version of the index, it should increase every time and be deployed to the detection servers. This is how you can verify if the index is generated or not. You can verify index version from System - Settings - Directory Connections - Click your directory Connection - Index and Replication status tab.
This is a cosmetic issue and is addressed in DLP 16.x. The only catch is you have to save the index first if changes are made. Then go back and refresh the index. If you make changes to the user group and refresh at the same time, you will get the RSOD and changes will be lost. So always save the changes first and then reindex.