I have this same problem when I run several lengthy scripts together (about 8 hours of test time). It seems Test Complete hits the 2 gig 32-bit cap and force closes. I've tried using CollectGarbage(); in several places, but still run into this. My only work around thus far has been to split up my scripts and run only 2 or 3 at a time. Mainly seems to fail while pushing out large arrays, and it "seems" as though the garbage collection isn't happening fast enough despite by usage of the CollectGarbage() function. This only started when I switched from using VBScript to JScript. Aside from magically coming up with a 64 bit version of test complete i'd be interested if anyone has a solution to this.
