[Brad Hunka]

Try this…

Enable “Secret” settings under EDIT/PREFERENCES. To do this:
– Hold down ALT+SHIFT while opening EDIT?PREFERENCES, select “General”
– In preferences dropdown, select “Secret”
– Check Disable Layer Cache and set to purge every 60 fames.

What this will do is purge the layer cache while rendering, not allowing you to overtax your system on multiple renders. I used to have the same issue as you and this resolved my problems.

Cheers, hope that helps!