Grasshopper not Installing Correctly on Rhino v5 64 bit

An error occurred during assembly parsing. Plugin may not function as expected

Mscorlib: could not load type ‘rhino.geometrey.MeshParameters’ from assembly  ‘rhinoCommon, Version=5.0.15006.0, culture=neutral, PublicKey Token 552281e97c755530

i get this message when rhino starts up. the plugin loads, but there are no components in any of the menus. how do i fix the problem?