Are you using MFFS2 or MFFS3?
If the forcefields appear instantly when you turn the projector on, you're on MFFS2 and the item you need is the MFFS wrench thing whose name escapes my memory. Shift-click it on air until it's set to the mods with a big green arrow, then right-click it on the forcefield. If have the necessary permission (if you're using the security system) (or if you set that one button in the projector GUI to the green mode, which shows an arrow passing through a wall), you'll be teleported through.
If the forcefields take a few seconds to appear one block at a time, you're on MFFS3 and all you need to do is sneak, and you'll pass right through the field blocks as if they weren't there. However, in this case, you almost certainly will need to use the security system. I don't remember how to do that off the top of my head, so your best bet is to look up "MFFS security" or something similar on YouTube and find a video with blocks that look like the ones you have.