Did you ever figure this out? If not, what Communication Type are you using within the Drive Space monitor?
If you open the Drive Space Monitor for the C: drive and then click the "Select" button, does it list the other drives?
Let me know,
Chris Foley - SolarWinds - Support Specialist
Support:866.530.8040 || Fax:512.857.0125
network management simplified | solarwinds.com