Make sure that BuildCraft's fake player, [buildCraft], has permission to build. Plugins like modifyworld and protection plugins can stop BuildCraft destroying/creating blocks in certain areas. You can do this by adding the modifyworld.* permission as an example to [buildCraft]'s permissions. You can also /op [buildCraft], but cautious if doing so. The same applies to [RedPower] and [industrialCraft].