Backing up Lotus Notes Domino server

I am having a problem when backing up my Lotus Notes database(440GB)in that is crashes the domino server from time to time.I also am running St.Bernards open file manager ver 8.0. The backup software i’m using is Syncsort Backup Express ver 2.1.4. THe Lotus Notes Domino version is 5.0.8.Does anyone have any ideas to what could be causing the server to crash during a backup?