Some systems don't even pick up the glideslope if you are too low or too high.  ILS looks like a sideways tornado funnel, in terms of the reception range.

The glideslope of the ILS 36R KCLT is at 2300ft at 5nm distance.  Try a more elongated approach into the ILS 36R KCLT, meaning intercept the glideslope at 7-10nm, or at around 3000ft.

Also make sure your NAV/GPS switch is set to NAV.

May not solve your problem, but it's worth a shot..

Above info is helpfull, another good way to be pretty sure you will intercept the ILS properly is to add 2800 feet to runway altitude and be at that altitude at least 10 miles out, maybe 12 or more miles just to be SURE.
a 'standard setting' of 3000 feet is OK for coastal locations but if runway altitude is 2000 feet above sea level your approach altitude would be 4800 feet. My experience is that if you are much higher than that you will never ctch the glide slope.  What was not mentioned above and may be most important of all is if your radio is set to HAVE a glide slope, look for this is your aircraft.cfg file:
[Radios]
// Radio Type = availiable, standby frequency, has glide slope
Audio.1=1
Com.1=1, 1
Com.2=1, 1
Nav.1=1, 1, 1
Nav.2=1, 1, 0
Adf.1=1
Transponder.1=1
Marker.1=1
You MUST have that 3rd 1 under Nav.1, as stated in types the first 1 indicates that you have a Nav 1 radio the second may be either 1 or zero depending on if the radio used in the cockpit has stand-by freqs or not and the 3rd 1 indicates the radio can catch glide slopes - if that 3rd 1 is missing or set to zero that would cause the problem you decribe.

Just to add to the pot, you may run into a backcourse ILS approach.  This is essentially a localizer reversed, with no glideslope.  Definately fun to fly 

In FSNavigator, backcourses show up like a full ILS does, but the wider end of the "cone" is pointed, not flat, as in the full ILS.  You can double check this by placing the mouse over the suspected backcourse runway, and bring up the stats.  If there's no glideslope height information, then it's a backcourse, or some other form of mutated ILS.