Unfortunately, a variety of issues can cause this error. The best route is to open a support ticket so we can look at your exact error and provide you a fix.
If you want to find the error yourself you can look in your OrionWeb.log file located in:
C:\Documents and Settings\All Users\Application Data\SolarWinds\Logs\Orion
or in 2008
C:\ProgramData\SolarWinds\Logs\Orion