I have also been unsuccessful with RNAV/172 landings. Tried to capture a number of Glide Paths at various airfields at the fix and altitude specified on the approach plate and when I hit APR for the autopilot (G1000) the AP goes nuts. After seeing some clues on Avsim, tried capturing at a lower altitude...still no "GS" capture success until the diamond came above the center, which was 500 AGL (+/-). Note: X-Plane G1000 RNAV on 172 works perfect if one hits APR just when fix is crossed at specified altitude on the plate...also indicates "GP" on the AP status line, rather than "GS" on MSFS 2000. Seems like a major bug needing a patch, hopefully in the next release.
