The validation error comes from the Rule-Portal.Validate activity. When the portal is configured with a Developer role, the code checks the .pyHeading.pyLandingMenu property. In this case it is null so the error is generated.
It looks like this is an older portal though. What version of Smart Investigate and Pega are you using? Can you use the Developer portal instead for your administrative access?
I am looking at a Pega 7.1.9 system with Smart Investigate installed. The OOTB sysadmin access group includes the following portals: Developer, SIManager, SISupervisor, and SIUser.