I have not had any problems with Toontrack plugins but have just had one with an Eventide 64bit plugin.
I have solved the problem.
What I did was go into the VST folder and change the name of the dll by adding on letter to it and rescan the VST's. The 64bit dll was then recognised by SonarX2a. I then changed the name back to original dll and it was still recognised.
It is strange why Sonar X2a should not recognise the dll in the first place.