I was using a sennheiser G2 kit (portable RX and TX lav. mic) the other day on freq. 792.600mhz.
Used in a new housing estate I could get a good 100-150m great signal and no dropouts, the following day same setup, inner city house it only dropped out at the back of the house and way out of shot.. good for 50m+. The next shot inner city street same person same mic position (hadn't been taken off) I struggled to get 2m range without dropouts, we did several takes to get what we needed. so all ok in the end. Battery indicator 3 bars full on TX & RX.
Anyone else had similar problems? I know its in the freq. band that is to change soon but I was surprised at the VAST difference in locations.

Always re-scan or at least check for extraneous RF (w/ transmitter off) at every new location.. unless within a kilometer or so.
Walls, metal objects, electrical devices, carbon-base lifeforms, ect. can reduce range.
Try to maintain 'line-of-sight'.

When performing an AutoScan with the G2 units, the scan only occurs in the current Bank. You may want to jump from the current bank to one at the other end of the spectrum if you're not getting all "4" free after performing an AutoScan.
Also try making sure that the antenna is pointed vertically - either straight up or straight down for maximum range. One more thing, check your Squelch. Check the Sennheiser website to see if there are any TV or radio stations broadcasting. You'll want to stay in the empty areas of the spectrum. Here's a few more tips in some videos I produced:

Sennheiser Wireless Tutorial on Vimeo

Super high quality Wireless microphone set-up for church, school, corporate, or live event on Vimeo

Sennheiser Wireless G2 hot shoe set-up on Vimeo