I'm having this same problem in VE Pro 7 Server (1056) with Win10 Home.
VE Pro Standalone works, but not VE Pro Server. I only have a 30 day demo key and I'm trying to make sure that everything works before considering purchasing.
When trying to "Insert Synchron Player" in VE Pro Server 1056 (which runs fine on it's own and as a plugin in VE Pro Standalone) I get Toolkit: could not open plugin
Same thing happens if I Insert Bus, and try to load the "SV Player"
Syncron Player v2046 launches fine by itself separately.
Tried uninstalling/reboot/reinstalling. No change.
Suggestions?