I hate to hijack the thread, but I'm in the same situation as the OP.
I was able to successfully install to two workstations, but then the next two are showing that the activation failed. I've tried uninstalling and reinstalling, pushing the activation from the ERA tasks, and attempted the activation methods available at the actual workstation. All methods failed and the activation process form the workstation actually gave me an "ACT.21" error.
Was there any resolution to this?