Try updating all Nvidia drivers and Physx. You should go into your folder C:\Programfiles OR Progfiles x86\nvidia\physx i dont know the exact path but it most likely will contain thoes words. Annyhoe there should be a updatephysx.exe in there or update.exe in there try running it or go http://www.nvidia.com/Download/index.aspx?lang=en-us
And select your products to check for the latest drivers. If you are running other GPU's then Nvidia that might be the issue since they tend to make they're software Nvidia compatible whitout issues.

I'm using an ATI card, not nvidia. I'll try updating it, I guess

Well that already can be the issue. Try updating tough. But most of the times specially with Nvidia software engines enc its because you dont have a nvidia card.

Can you please upload .midmp and .bidm file too? When file will be too big, so please use some free sharing service and write link here. Thank you.

http://puu.sh/3zXlY.mdmp
for the minidump, I added the bidmp to the uploads

I am also having the exact same issue with Physx3_x86.dll. Game keeps crashing after 30 to 60 minutes. I use the ATI Radeon 5870. Enclosed the .rpt, .mdmp, & .bidm files from the last 3 crashes.

http://www.4shared.com/rar/h_vx9L2N/Arma_3.html

Here is the dxdiag log

http://www.4shared.com/office/Ml60f59z/DxDiag.html

This did not happen in alpha at all.

Never had this issue until the update today.
Faulting application name: arma3.exe, version: 1.2.110.424, time stamp: 0x52440456
Faulting module name: PhysX3_x86.dll, version: 3.2.4.1, time stamp: 0x5164246f

Issue closed as obsolete. If you encounter this problem again, please create another ticket. Thank you.