ESET Endpoint Security installed from ERA won't activate

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I've been able to install 3 other workstations using the ERA console with no problems. Today and yesterday I was installing more clients and each time the installation ends up reporting that the product can't be activated.

I've tried a "product activation" task from the ERA with the license assigned to it and it fails. I've also tried the numerous activation options that are available at the client in the ESET app and they fail as well. The only error message I've been able to get is a code "ACT.21" which I can't find a reference to anywhere on the support site.

 

I haven't changed anything in the system since the first two successful installs, and all targets are Win7x64. What am I doing wrong?!?