Meshing Error in Creo Simulate when Changing Component Orientation

[ptc-1420133]

I am using Creo Simulate Release N/A and DatecodeN/A

I am running a simulation on a two piece aerofoil. The applied pressures are entered via .fnf files generated using Creo Flow Analysis. The aim is to run a baseline configuration and obtain the Fx and Fz loads to give lift and drag. The next step is to vary the angle of the aerofoil flap and compare the values for Fx and Fz to baseline.

Unfortunately the assembly will run in baseline configuration and with the flap angle increased by 1 degree, but fails if the flap angle is reduced by 1 degree. This happens at other angles too but I cannot see why.

Here are the errors that I faced
Singular mapping, solid element: 1345420

The design study terminated abnormally.
The element with DBID 1345420 has invalid geometry.

[ptc-1420133]

Below is a screenshot of the error:

The element which causes the failure is inconsistent, i.e. if I run the analysis again, it might be another element which causes the failure.

I had wondered whether the issue was the constraints for the flap element which join it to the mainplane but I've tried bonded joints and adding an additional central fixing and haven't found a solution.

Currently the only constraints linking the flap to the mainplane are those within the assembly: 

Not sure if these are sufficient to ensure the assembly works within simulation?