FEA analysing the Framework extension design (Formula Student Chassis Frame).

Hello everyone.

I am designing and analysing the Chassis frame with Creo using the Framework extension.

I am struggling to analyse it on Autodesk Simulation Mechanical.

The error i get on Autodesk Simulation Mechanical:

ERROR NUMBER 150:

Input surface mesh does not enclose a watertight solid.

Have highlighted (LAYER=2,3) sides of holes in surface mesh.

How do i fix this inside Creo???

Any ideas?