You have some geometry which is not allowing the software to perform a Boolean operation to extract the fluid volume. Bad geometry is a most typically a zero area contact condition, such as an edge or vertex just touching a surface. Also think of two circles just kissing each other at a point.
You can remove this bad geometry by separating them, or you can create another dummy volume over top of the place where the zero area contact occurs.
Or, also it could be that you only have Surface bodies. Flow Sim requires solid bodies to run.
See this post: Flowsim Help: Typical Issue with surface body and geometry
On the first tab of the general settings, you need to select external as the analysis type. Right now its set to internal and flow simulation can't find any passages for fluid to flow inside your model.