Goto Administrative Tools-> Services and stop the SolarWinds Orion Toolset Integration Service and then click 'Retry' in the install dialog.
The new 10.6 version of the Toolset has an integration service that runs in the background. Make sure you've stopped ToolsetIntegrationTray from the Task Manager before uninstalling. Also, make doubly sure that you are done with your evaluation. If you plan to reinstall the evaluation (and not a production copy) after removing the eval, you could have problems. If you do, just make sure to touch base with the sales team over at SolarWinds so that one of the Sales Engineers can help you through it.
Doh, Steve beat me to the punch. Now you've got two suggestions. ;-) Hope that helps. Thanks Steve.
Thanks very much for the quick reply. This worked fine.