Properties and flextables will not open in WaterGEMS/HAMMER or SewerGEMS when integrated with ArcGIS. This may impact other managers, like the scenarios or alternatives manager
First, make sure that you are using a compatible version of ArcGIS. See the compatibility chart to see if your version of WaterGEMS, SewerGEMS, or HAMMER is compatible with the version of ArcGIS you are using.
If so, trying running a repair on WaterGEMS/HAMMER or SewerGEMS through the Control Panel. To do this, open the Control Panel and go to Programs and Features. Find WaterGEMS/HAMMER or SewerGEMS in the list of products, highlight it, and select the Repair option. This will reinstall key components and reintegrate the product with ArcGIS. Once completed, the WaterGEMS or SewerGEMS managers should be available.
WaterGEMS for ArcGIS FAQ
SewerGEMS for ArcGIS FAQ
Project manager will not open in ArcGIS integrated product