Coming back to RUS after a few years away, and bought & installed RUS Gold. Was getting crashes as above every few turns. Couldn't remember anything like this with RUS, so installed this, patched to 1.04 and than noticed 1.06a so patched with this as well. As I thought ran with no problems.
Preferred RUS Gold to RUS so I ran this again. This now ran with no problems and has been crash free for 3 days. So it may be that something that RUS installed is also required by RUS Gold, which would explain why none of the developers can reproduce the problem.