Saving of Custom Reports throws error:

"500 - Internal server error. There is a problem with the resource you are looking for, and it cannot be displayed."

In the Manager Service Log you find:

15:17:36 1 - Report Scheduler - :

An entity could not be initialized because exactly one row was not returned
from the underlying query.
NetQoS.Business.i18nEntityInitializationException: An entity could not be
initialized because exactly one row was not returned from the underlying
query.
  at
NetQoS.Business.DatabaseEntity.InitializeFromQueryResults(DatabaseEntity
databaseEntity, DataTable table)
  at NetQoS.ReporterAnalyzer.Business.User.GetByName(String name)
  at NetQoS.ReporterAnalyzer.Business.ReportScheduleItem.Set(DataRow dr)
  at NetQoS.ReporterAnalyzer.Business.ReportSchedule.GetUnscheduled(DateTime
utcNow, Double minutesOverdue)
  at
NetQoS.ReporterAnalyzer.Business.ReportSchedulerThread.CreateNewSchedules(IEma
ilSchedule schedules)
  at NetQoS.ReporterAnalyzer.Business.ReportSchedulerThread.ThreadHandler()

Release:
Component: NQRPTA

For NFA 9.3.x and up:
       1. Create a user called "admin" with Administrator privileges under "Users" in the NFA Administration GUI.

For older NFA versions without  a GUI to create users:
        Add "admin" user to the reporter.user_definitions database table on NFA and add "admin" user manually to NPC.

1. RDP to NFA console server
    
2. Open command line
    
3. type: mysql reporter
    
4. type: INSERT INTO user_definitions (UserLevel, Name, Description, Password, Algorithm, AuthType, Enabled, Removable, ExportURLs, FirstRun, RoleID, PermissionID, EmailAddress, Timezone, UpdatedOn) VALUES (1, 'admin','ReporterAnalyzer Administrator', '21232f297a57a5a743894a0e4a801fc3' ,0, 1, 'Y', 'N', 'N', 'Y', 1, 1, '', 'GMT', 0);
    
5. restart the NFA console server
    
6. If NFA is connected to an NPC, go to NPC UI and add the missing "admin" user manually (if this is not done, a full re-sync will delete the user from reporter.user_definitions again)