The error message  "System.OutOfMemoryException" means that SAgent service has consumed all allocated memory. 

The following factors cause the issue: very large backup set - TBs, limitation of memory usage on 32-bit operational system.
It is necessary to check the amount of used memory on the affected device.

1) For this press Windows +R, type Resmon.exe 

2) Go to Memory section and locate the process SAgent.Service.exe

3) Collect the amount of used memory by the SAgent.Service.exe process.