As it turned out, Macworld Expo was just around the corner. While there, I brought up this incident with some friends. One of them had had the exact same thing happen. After some discussion, we concurred that the immediate cause was almost certainly a bent wire in the battery's dock connector. From a brief inspection of the 1200, I could see no obvious damage, but I assumed it was there.

In my case, I assumed that the damage resulted from unintended pressure applied while the connected phone and battery resided in my pocket. Problems with the dock connector are a known source of the "accessory is not made..." message (as noted in this ). I suppose I should consider myself lucky that the damage was restricted only to the Solo battery's connector and not to the iPhone itself.

As for the completely drained iPhone battery, I can only theorize as to the cause. My friend suspected that the damaged wire may have led to a reversal in the direction of current flow, so that power was going from the iPhone to the battery instead of the reverse. I can't confirm this, but it would certainly account for the symptoms. I contacted RichardSolo.com for a reply, but did not receive an answer.

In any case, I've learned my lesson. In the future, whenever I have any accessory connected to my iPhone, it will staying far away from my pants pocket.