One reason that cause this to happen is if you have another audio application that runs VST plug-ins installed on the same computer. For example, having Sonar or Cubase installed on the same PC can cause this type of problem.

Here is one work around to get Vegas to load properly.
Go into the Program Files folder, then into the folder of the other audio application (not Vegas), and remove the VST plug-in folder and place it on your desktop.
Launch Vegas. When finished using vegas simply put the VST plug-in folder back in the application where you found it.