Error backup Exchange DP VSS API 3

Hello

I've a problem on my job to backup exchange server.

I'm on version 8.10 (before I was on version 8.00 and it worked).

I've the message

Error 3 returned from DP VSS API

On all client Firewall is off. On each client in omnirc.tmpl I add 

DPCOM_SWITCHUSER_TIMEOUT=600
DPCOM_CONNECT_TIMEOUT=600
OB2IPCKEEPALIVE=1

But the problem is still present.

I haven't got allow-hosts in C:\ProgramData\OmniBack\Config\client on my client and I check  for Show hidden files,folders, and drives

I have not ideas what I've to do.

Thank you

I can't restart servers