Status code 9 after applying pre-load to connectors

Hi !

I am running a simulation for an assembly with SW2012. Parts are connected with bolt connectors.
At first, there was no pre-load in the bolts. The calculation succeeded using the iterative solver.

Then, I added pre-loads. Now I am getting a Status code 9 (matrix singular or ill-defined). It says I should use the Direct solver, which I tried, but I'm running out of memory to complete the calculation.

Any suggestion about how I could make this work with the iterative solver ?

Thanks

Astrid.

SolidworksSimulation