Hi, Rob.
Initially, I'v think the same - PHP memory limit is not 64M. But I and my host admin have checked, perhaps, all of places. Everywhere, the memory limit is set no less than 64M.
We try also to set limit highly - 128M and so - the same error was present.
Some time ago, I had the similar error. And at that time, I'd revert to initial 2.0 release - that error had dissappeared. And at last (not just the last, but at the previous to) version, I'v got that error again.
And also one strange thing. Onсe, I had luck to kill that error by that way:
1. Unlink group from the form.
2. Remove all elements to new group
3. Link that new group to the form back
4. And it starts to work!!
(But error returned in 1 or 2 days in other form)
I hope, that this detail will help you fix this error and make the Fabrik more better.
Now, I'll try to revert to
SVN
2421 and look, what will happen.
AlexV