Hello,   Most likely it's because there is a CHAP ACL on the vss-control volume.  When the remote setup wizard is used to configure the array it asks you to create a CHAP username/password.  It uses that for the ACL on the vss-control volume by default. If you remove that CHAP ACL the error will likely go away.  Regards, 
I finally got around to setting up MPIO for an NTFS data volume on a Windows 2008 R2 vm to my EQ group, but I'm getting an error "VSS control volume is not accessible from this host". On the EQ, I have VSS access policy set for IP to accept the whole subnet.  The error notifications from the EQ includes "CHAP user grpadmin authentication failed", but I'm only using the IP access, not chap. CHAP is optional, right? It's a private subnet on internal switches.  Also, in the PS Group Access, "Use Chap credentials for iscsi discovery" is unchecked. In the MPIO host view, the iscsi connections shows "2 ok, 2 bad." I only have 2 nics on this vm. Edit: Also, in the group access window, the VDS/VSS access has a green check mark.
VSS Control volume error with HIT/ME