I was having major problems also, with a fresh reinstall. I ended up reinstalling about five times before I got stable. Actually I was making copies of the entire folder and kept reapplying the RSII install until I got a working one. I install to C:\RSII.
Originally I had RSII version 2.0 install some months ago. I had everything turned on, including high vegetation and high res units. I upgraded to 2.5 without problems, but my RTW install had several other mods installed and I wanted to get a clean RSII only install.
I'm also running Windows 7, but not the Steam version of RTW. Just RTW and BI, fully patched. I'm also running Microsoft Security Essentials for antivirus. It does not seem to be causing problems. There are two variables that I changed;
- This last install I first installed only version 2.0 and played into a campaign without issues. I did not touch any graphics settings, in game or via the launcher. Then I went to 2.1a and played a few more battles. Then I installed 2.5 and have started an Armenian campaign. I'm now five years in and have five or six battles, most of them major, including a city taken by me. Previously I was skipping from 2.0 directly to 2.5. This last time I want 2.0 to 2.1 to 2.5. I don't think it's that, but it is a variable.
- Because all my settings were maxed on my old install, and it would work on version 2.0, previous installs I turned on AA, high settings for graphics, vegetation and high res units. I would turn them down when I got to version 2.5 after experiencing CTD post battles. This time I have not touched these settings at all. I've left them on default settings.
If I go a few more turns without any crashes I will boost all the graphics settings to high via in-game menu, not launcher. If it still continues to work I will add in high res units again from the launcher, and try for CTD's again. If it STILL works after that I will enable vegetation. I'm hoping to pinpoint my failure. I suspect it has something to do with these settings being previously enabled in version 2.0, and even though I would turn them down/off after upgrading to 2.5, something was still being left in an "enabled" state. I am determined to get my settings as high as possible, I want to have my cake and eat it too...