Big stack memory question

[FlexibleLearning]

We have an open 'destination' stack (2Mb) that sucks in data from a closed
'source' stack (894Mb). The closed stack is loaded into memory in order to
transfer its data with 'set the customproperties of DestinationStack to the
customproperties of SourceStack'. The open stack grows as it receives the
data. When finished, its size matches that of the source stack, and the
source stack is deleted from memory.

Question 1
Using a WinXP 32-bit computer with 3.25Gb ram, we have no problem.
Using a Win7 64-bit computer with 8Gb ram we get "Can't find stack".
Actually means "run out of memory to fully load this stack", but why won't
it load? We can load a smaller source stack, but LiveCode stops responding
when the destination stack gets too big.

Question 2
How can we tell if there will be a memory problem? Can it be
programmatically calculated to pre-empt the problem?

Hugh Senior
FLCo