I tried to reproduce the error you are getting, I am using V27.2 and when i run V28.0 root.v4p works fine. So, i unregistered V27.2 and registered back with V28.0 now root.v4p throws up error message.
I have attached the log i got, hope it helps to understand the bug.
the error when starting vvvv via double-click on its _root.v4p is unrelated though and is more a warning than an error (that only pops up in the alpha builds anyway).