You need to look into this error.
Monitor your Committed memory usage. You can find this with Task Manager → Performance → Memory.
Look toward the lower middle section for Committed. This shows your Virtual Memory space.
Watch that while playing. If that gets to where the two values are nearly equal, your game will crash.
You can also pull the fenris log after you crash and near the bottom it will show how much physical and virtual memory you are using when it crashed. If you fill up the virtual, you will crash.
There are ways to prevent it, and it may not help everyone, but it certainly won’t hurt to try it. But check to see if its an issue FIRST before jumping to make the following change:
-Diablo IV has run out of memory - #103 by DTMAce-1687
One recommended difference from the above fix:
Use a value of 32768 for the Min and Max page file setting as described above. That post was provided a while back under different circumstances.