Business Console - Error checking task engine status

Our BusinessConsole (https://:9095/rest/bc/connectivity/taskEngineStatus) keeps reflecting the following error:

Error Exception in Task Engine: null

and when viewed in developer tools we find:

rest/bc/connectivity/taskEngineStatus:1 Failed to load resource: the server responded with a status of 500 (Server Error)

The IS TaskClient is properly configured, the MWS server is properly configured (as far as Administrator pages allow) and the tasks are indeed visible when looking directly into MWS…

Anybody any constructive suggestions?