VERIFIED SOLUTION i
'Encountered an improper argument' error is observed when the ActiveX tries to call an Active Content group.
This is a defect in ActiveX 126.96.36.199 which is being used by EngageOne Server 4.4.5.
ResolutionUPDATED: August 31, 2018
This has been resolved in ActiveX 188.8.131.52 and EngageOne Server Version 4.4.7. Hence, upgrading to these or later releases should resolve it.