It sounds like Internet Explorer is tripping on something, but just to be sure, can you check to see if the "SolarWinds Discovery Service" service is running. If this service isn't running, ipMonitor will wait a long time for it to discover devices.
Also, can you perhaps try scanning your network using ipMonitor via Firefox and see if you get the same behavior?
Let me know,
Chris Foley - SolarWinds - Support Specialist
Support:866.530.8040 |Direct:512.682.9385 |Fax:512.857.0125
network management simplified | solarwinds.com