Respondus 4 and external SSO - This action cannot be completed because the other program is busy.
Posted by Respondus Support

For Respondus 4.0 Campus-wide accessing a supported LMS with an external single sign-on portal, a warning of:

This action cannot be completed because the other program is busy. Choose "Switch to" to activate the busy program and correct the problem.

appearing after authenticating through the SSO, indicates Internet Explorer 11 is not available on a Windows 10 system.

A quick check is to right click on Windows 10 Start, select "Run..." and enter "iexplore" or "iexplore.exe".

If you cannot find and start Internet Explorer with "iexplore.exe", it indicates the feature has been turned off. You will need to have Internet Explorer 11 available on the Windows 10 system.

You can go to Windows 10 Start->Windows System->Control Panel->Programs and Features->"Turn Windows Features on or off" then check "Internet Explorer 11" as seen in this screen capture: https://screencast.com/t/85KzU8c3BK