Larry Jordan gives this explanation which can help, but often doesn't solve the problem:
The main reason I get this error is when using large still images. Big ass monkey images like 5K or summut.
For years I have searched for a solution online and in the ether to no avail. However, yesterday I was told a very simple solution.
Go to Sequence/Settings and click on the Video Processing tab. In here you will see that the default is to render in 10-bit. Changing this to render in 8-bit seemed to solve all my memory issues.
Oh and by the way rendering takes about half the time in 8 bit mode.
Good luck people, and stop using 7 anyway.