This problem exists since the release of Update 2 but I still get a lot of questions from collegues who run into this. After you upgrade your VirtuaCenter version 2.5 Update 2 guest customization stops working. When deploying virtual machines from a template sysprep does not run after the first boot. I had to first manually login and then they would start or after waiting a really long time without login. This is a known issue and will be fixed in Update 3. For the time being VMware released a fix in the following kb article.