From what I've tried and also gathered from reading the forums here, a positive adjustment will add points to one's EP, and a negative adjustment will add points to one's GP.

What I'd like to do is reduce a player's EP by 250 when he/she signs up for a raid but doesn't show. Is there any way to make such an adjustment or do I just need to subtract 250 EP from the next raid that person attends?

Interesting. That's not something I've thought of. You're right, as of current, you'd either have to modify a new raid to be 250 less points, or you can go back and modify a past raid to be 250 less points. Either way, it's not terribly intuitive. The EPGP support is scheduled for some significant upgrades.

Okay cool, thx for the reply and I look forward to the upgrades

We use the EPGP system as well and just do a one time adjustment (-250) for the person who gets approved for a raid and doesn't show. The adjustment has an info box that you can put in which raid it was, date, and what they did (didn't show, retracted signup after approval, etc.)

Not sure if that is what you are looking for but that is how we get by.

That's what I'd like to do, but when I do a -250 adjustment from the "Adjustments" link in Admin it adds 250 GP to the person instead of subtracting 250 EP.