Guest customizations fails after upgrade to VMware vSphere 6

VMware vSphere 6 is now an year old and it was time to update my lab to vSphere 6. The update went smooth, and everything has worked as expected. Some days later, I updated the master VM of a small automated desktop pool. I’m using VMware Horizon 6.2.1 in my lab to deploy a small number of Windows 8.1 VMs for tests, administration etc. The recompose of the pool failed during the guest customization.

I checked the customization specification immediately and got an error in the vSphere C# client.

Interestingly, I got no error in the vSphere Web Client:

After re-entering the Administrator password, the  customization specification was usable again. No errors so far.

A quick search in the VMware KB lead me to the article “Virtual machines with customizations fail to deploy when using Custom SSL Certificates (1019893)”. But this article doesn’t apply to vCenter 6.0. For the notes: I’m using CA-signed certificates in my environment. It seems to be a good idea to re-enter the passwords in customization specifications after a vCenter migration/ upgrade (5.x to 6.x or from VCSA 5.x to 6.x).