My question is, does this sound like a Sibelius issue or a communication error with the write score template?
It's a Sibelius issue. If it was Template related, everyone
would be having that issue, including me.
Was this downloaded from Tapspace? It may be better to use Kontakt Player 5
in either case.
1) Get KP5 going.
2) Close Sibelius. Delete the entire "Playback Configurations" folder from the User's directory (same place as Sounds
folder). Start Sibelius. Create a new configuration with one instance of Kontakt Player/VDL. Open a TriggerTest file, hit Play. Go back and add another instance of KP/VDL to the config, proceed.
3) Do a full re-install of Sibelius.
Be systematic in your approach, i.e. try one thing at a time. Oh, and make sure to attach a screen shot of your Playback Configuration(s).
Let me know how it goes.