Hi
I have the same recurring problem as you.
Eg Making reference QT of 40 min HD timeline to make draft DVD. I get Out of Memory Error
My workaround has been closing all other seqs and bins, restarting machine, opening and rendering without doing anything else.
Reluctant to keep messing with the card but if it works will do so as it is so so frustrating.
Nb Just spoke with my Kona/sytem supplier who is seeing this problem alot with and without Kona cards. He says I may actually need more ram than the 4gb I have.