Hi Rechelle,
OK, so Pacing is a comparison of predicted vs actual dialing.
Say, for example, the algorithm has determined that you have an answer rate of 1 in 3, then it will place 3 calls every time an agent becomes available. In this condition, the Pacing is zero.
OK, so say that suddenly the contact rate goes up. The Abandonment rate will go up. Dialer will respond by essentially saying "I think I need to place three calls, but I'm only going to place two." this is known as reducing the pacing and results in the negative numbers you are seeing - notice how they correspond with the high abandonment rates? This often occurs when the contact rate is not consistent across the call list - a common cause of this is sorting the call list my something geographic, causing local conditions to affect the contact rate. (Weather, sports events etc.)
In 3.0 (and before) you were able to manually adjust the pacing, but folks would start messing around with it without understanding what it was actually doing - the result was that they were constantly "fighting" the algorithm. (Often increasing the pace if they perceived idle agents, rather than trying to figure out why the agents weren't getting calls. Thankfully, the control was removed in 4.0!
I hope that helps.