The problem is caused by the fact that the projector apparently draws a small amount of current even when it is "off", and you are using a control plug that has the local control feature. This feature is mainly intended for use with lamps, where the lamp is plugged into the X10 module; by manipulating the on/off switch of the lamp, you can turn the lamp on without using the X10 controller.
What you need to do is modify the X10 plug to deactivate the local control feature, or buy a new on that does not have this feature. Such units are made by Leviton and ACT. The modification is very simple; just cut one wire (if I remember). I don't know where the instructions are now, but do a search on deja.com for "x10 mod" and you'll find it.