If you see this error, it usually means that there is a surface that Rhino is having trouble meshing.  

You can first try selbadobjects and if Rhino finds anything, delete them. 

Sometimes it can be resolved by changing the mesh settings. To do this, in the Orca3D Hydrostatics & Stability dialog click on the Adjust meshes button, then click Detailed Controls. Try adjusting the Maximum aspect ratio to 3, the Minimum initial grid quads to 500, and finally be sure that the Minimum edge lenght is reasonable (e.g., something larger than the Absolute Tolerance that you have set in the Rhino Document Properties under Units).

If that does not resolve it, the next thing to try is to explode the polysurface, and then run hydrostatics. You may get one or more errors like this:

Type the command selID and enter that ID. Then delete that surface and try again (note that while you cannot copy and paste the object ID, you can copy the entire message with CTRL-C, paste it into Notepad, and then copy the ID; this saves manually typing that ID in the SelID command).