Repro: attempt to convert a 192kHz/24bit wav (7 minutes long) into 48kHz/24bit source file is large (510.11MB), but not particularly long using AudioFinder 5.3.3
Result: Error: Signal Processing effect encountered an error: "Not enough room in heap zone / (-108)
This is a known design limitation. It's covered in the manual, AudioFinder is designed for managing sample and track length material at reasonable sample rates. Anything over around 500MB requires a dedicated audio editor.
...and actually is is particularly long, data-wise, that's a full CD worth of PCM audio data.
in any case those limits are going to be removed in the future once as AF fully migrates to 64 bit.