Encountered this problem recently while I was migrating a vSphere environment across to newer hardware. I needed to migrate a template across which required converting the template back to a VM, then using Veeam migrating across to the new vCenter, once there I converted back into a template. Also along for the ride were a couple of guest customization scripts which I exported from the source and imported on the new hardware. Easy right?
Unfortunately, whenever I tried to deploy a VM from this template it threw the following error “Customization of Windows guests fails with the error: Customization of the guest operating system ‘windows7Server64Guest’ is not supported in this configuration”. Now VMware does have a knowledge base article on this problem but it simply asked me to install VMware tools. Well, VMware tools were already installed. I found another suggestion here Pepper Crew Blog but that did not solve the problem either.
What ended up solving the problem for me was converting the template back to a VM, powering the VM on then updating the existing VMware Tools to a newer version. Once I had completed the VMware Tools update it had resolved the problem.
Link to VMware Knowledge Base Article: http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=1020716