Hello all, got another email from EA sometime in the last week (was away from computer for a little while). I thought they were going to ask me for my computer specifications again, but no, instead they thanked me for the "honesty" of my emails and assured me that they are working on the problems but that these things take time. It's the most sensible response I've had so far from EA and the one that's come closest to them confirming that our problems are on their hit list for fixing. I wanted to mention it here because via that email they are thanking us all for reporting the bugs on this forum and crinrict for helping us out.
BevH, I had invisible sims that were not created with those CAS sliders, so that patch may have caused glitches, but using the sliders was not the direct or sole cause.
I'm going to try the ErrorTrap that crinrict recommended to further clean up my game. Then I'm going to have a go at Twallan's Story Progression. I like the features that allow you to stop everyone becoming a celebrity or a vampire (or both). It also sounds useful to cap the town population. If Story Progression causes too much lag then I'll remove it, but it sounds great and I'd like to try it while I've got a functional game - thanks to Overwatch - on the go. I'll report back once I've got to grips with it!
