Probably because DVD Architect is really old and your DVD recorder is really new! Several new versions of DVD Arcitect have been released since then.
Here's what you might try:
PREPARE in DVD Architect
BURN using some other program like Nero or Record Now (not sure about "Windows DVD Maker" - should work if it can use the Video_TS/Audio_TS folders created by DVD Architect)
Edward Troxel