KDEN glideslope intercept screwed up

[ineedabetterplane]

Hi all,

I'm new to this forum and relatively new to FSX, so I don't have any add-ons or extension packs. Whenever I try to do an ILS landing at Denver international, my aircraft, usually a CRJ or 737, always picks up the localizer's signal and aligns me with the runway, but many times the autopilot will not follow the glideslope's signal.
When the controller clears me for the approach, I switch to the frequency on Nav 1, switch to Nav, press approach hold, and if needed, disengage heading hold. I do a manual flare and come in at about 143-150 knots. Am I screwing up somewhere or are there glitches related to this with the default airports/aircraft?

Any help would be welcomed. Thanks!