Hello Andy,
This is what SAP note says :
- Delete the 'DMUserSelection.xml' file from the machine in the location associated to the user that is experiencing the error message.
- When the EPM Add-in is next opened and the Data Manager is accessed, this will cause the EPM Add-in to regenerate the 'DMUserSelection.xml' file thereby resolving this behavior.
You should ask your company super administrators to create account for you so you can take a look at SAP notes.
-Yogesh