Azure Backup Server error: ID 4501

Try to completly reinstall The Single Instance Store (SIS) component

To uninstall Windows Single Instance Storage (SIS) In an elevated command prompt window, run start /w ocsetup.exe SIS-Limited /uninstall /quiet /norestart. After SIS is uninstalled, you must restart the computer.

To manually install Windows Single Instance Store (SIS) On the computer that will be your DPM server, open an elevated command prompt window, type the following command, and then press ENTER.

start /wait ocsetup.exe SIS-Limited /quiet /norestart

or

start /wait dism.exe /online /enable-feature /featureName:SIS-Limited /quiet /norestart

https://technet.microsoft.com/en-us/library/ff399781.aspx