Sysprep won't start

Hi!

I'm using ESXi 5.1 build 799733 and vCenter Server 5.1 build 947673

My problem is, when cloning or building a VM from a template, and using the customization tools, sysprep never start once I start the cloned VM. Never ever. No error messages, with both Windows 2008R2 and 2012 guests.

Any ideas?

Any way I can do it manually?

Thanks for your help!