I assume you are using 1.3 (latest) which is fine.
Go to Ian's noticeboard:
http://pub17.ezboard.com/biansmessageboard69920
and check out the DMute section - you might see the error that is causing your problems in your editing. Even if not it is a very good forum that has posts now gone from this board, with general advice.
A common lot seem to be:
a) Choosing too high a graphic number for doors, pressure pads etc. Some dungeon levels don't have any graphics for higher numbers (level one has no ornate 2 onwards doors, level three has no graphic 3 onwards pressure pads), which can cause glitches, or at worst crashes.
b) Occasionally objects/monsters get 'cloned' - existing on two or more tiles at the same time. Killing one creature while the other exists and is moving around can also crash the game.
c) The stairwell bug. An odd bug, the game hangs going down stairs. To solve it, have a teleporter From the first level to the last, and another from the last to the first. This cures the bug.
d) Changing the third byte of tile hex. If an object exists on this tile, then the byte is 10 larger than normal. If you have changed a tile and not taken this into account, it tends to alter every lower level of the dungeon under that level so it will crash (monsters in walls, etc) and will also crash when this tile is encountered.
Definately check out the DMute forum, most people on here post there too : )