A little more info would be useful. Teleporting in or outside of dungeons? Teleporting using magery or ninja (shadow jump?)? Teleporting in PvP or PvM? Which client? Anything else more specific would help.
In Tram there are some dungeon that do not allow teleporting. In Fel most dungeons allow teleporting yet in some spots its disabled.
Teleporting close to houses is disabled in all lands/faucets. I believe teleporting works much like house placement. You must be at least 3 spaces off the east/west sides and 3 or 4 spaces off the south/north sides.
In PvP using UOA you can set up macros for teleporting if you get dismounted. Mine are the arrow keys(N/S/E/W). I record a teleport 7 (maybe 6? I forget) spaces in a straight line then set it for "target relative". I can teleport off any direction in a straight line pretty quickly if I time hitting the key right so not to overcast or miscast.
Not sure if this can be done in the EC but I do know there are also scripts set up for this (many PvPers use them). In PvP some players use client mods that remove trees so they have clear lines of sight and never miss clicking the ground (as trees can get in the way).
There are many reasons for this depending on play styles and macro setup. Without more info it would be hard to determine exactly why you seem to have this problem and even with more info, it will prob be just as difficult