I've been getting this frequently on Provisioning Server 5.6.3. I'm not sure if the problem affects other versions. I was getting the MAPI error when changing a vDisk from private mode to standard mode. Other changes I was attempting to the vDisk properties was enabling Active Directory management and the Licensing Mode. I was able to get past this error if I did not change the licensing setting on the first attempt, save the changes, then go back into properties and set the licensing mode (KMS in my case).