Internal error occurred in vSphere Client

Hi I am getting a "Type serialized error" every time I try to add a new hard drive to an existing VM.

The exact error is:

An internal error occurred in the vSphere Client.

Details: The type serialized in the .resources file was not the same type that the .resources file said it contained.  Expected 'System.Windows.Forms.ListViewItem" but read 'System.Windows.Forms.ListViewItem+ListViewSubitem

\

any ideas?