vnc to thin os reduces display quality

 Hi,

When connecting to a 3010 / t10 thin client with vnc we have issues that the display for our vnc session is very low quality, and unusable.  We use this to support our users.  This doesn't happen with our dell 3040 thin clients, only the 3010's.  We tried multiple vnc clients.  It doesn't appear to be a vnc client setting.  The quality doesn't drastically reduce until the user is logged into their windows session.  Any suggestions?