VS2012 Express debug 4.3

Trying to debug a small problem

An unhandled exception of type ‘System.NullReferenceException’ occurred in GHI.Usb.dll
C:\Program Files (x86)\GHI Electronics\GHI NETMF v4.3 SDK\Libraries\le\GHI.Usb.dll: Cannot find or open the PDB file.

C:\Program Files (x86)\GHI Electronics\GHI NETMF v4.3 SDK\Libraries\le have

*.pdbx ?

No symbols found dialog options Files of type: only shows Symbol Files (*.pdb, *.dbg)

Why are the pdb files listed with x?

Just a question… No a issue

Thanks