The ‘SQLdm Repository Grooming Timed Out’ alert is triggered when the grooming process of your SQLDM Repository has reached the time-out period (180 minutes).
The time-out period is typically exceeded when the repository database becomes very large. Running a complete reindex of the database should help improve the performance of the grooming process and prevent SQL DM from raising this alert.
To review your grooming settings, go to Tools 
> Grooming Options.