Hi Mark,
> Is this happening after you've made any changes to your set-up?
(like: refining mesh, geometry, or changing any variable or values)
> If any changes are made, does your computer possess enough resources (RAM) to get the new set-up processed?
> Any other program running in parallel, that was not running before? - This might be taking up the CPU computing space that is needed to attain a solution.
Thank you.