Hi!
The issue here is simple: under normal circumstances for incompressible analyses, we need a single volume, representing the flow region, to run the simulation. If your CAD model has more than 1 volume, you will run into multi-region errors down the line.
The flow region, as I mentioned, is what we want. Solid1 is the part causing issues. The remedy here is very simple: head back to CAD mode, create a delete body operation and delete solid1.
The resulting model should be good to go.
Cheers