I've got force fields working in single-player just fine. I'm putting the right blocks together and have adequate power. They work sometimes.
I'm testing currently with just a core and a cube projector, for simplicity.
I got them working in SMP, but after using them for a day or so, and after a server reboot, they stopped turning on, except if enabled when the server starts. Later, they started working again, then stopped.
To elaborate: if I leave my force field(s) turned "on" (despite them not working) and the server restarts, my force fields will be active. If I then turn them off (with a wireless remote), I (usually) cannot turn them back on. The projector block takes on the "active" texture, but no force field blocks are created.
Some other players on the server have experienced no problems with their force fields. Some can't get them to work at all (probably aren't trying as hard as I am.) I've tried using them in several different areas with no change in how whimsically they function. I've tried destroying them and crafting new ones with no change either.
Sometimes I can turn a field on and off at will, many times in a row. Sometimes a field won't turn on at all. I've never had trouble turning a field off.
Please help?