Error 0xe00084f4 - unknown Error - ESX Server, HP SC11Xe and Ultrium Tape Drive

Good Morning , 

System Configuration : 

HP ML350p Gen 8 Server with an HP SC11Xe 1-Kanal Ultra 320 PCI-E Host Bus Adapter connected to an HP Ultrium 920 Tape Drive .

This runs under an ESXi 5.1 U1 Server . On this ESX Server is an Windows SBS2011 VM running . 

On the SBS 2011 is Backup Exec 2012 SP2 installed . The Tape Drive is visible in the Server Hardware and also in Backup Exec . 

The Tape Drive Test with "HP Libary and Tape Tools" runs without errors .

The Exchange Backup Job with 20 GB Data runs without errors .

The Data Backup Job with 166 GB Data ends with error :

 Error 0xe00084f4 - unknown Error 

The error appears sometimes at 3 GB , sometimes at 30 GB backuped Data . 

Thanks for Solutions . 

Michael