Thanks fellas for the replies, I appreciate it.
I emailed them and they stated that the $10 charge they charge me every month put my account in a debit balance. In other words, talk about timing! The following day, I entered a trade, it happened to reverse on me, and triggered this call.
It makes sense -- It's just that two things had to occur that had to occur to make this happen:
a) The $10 charge occurred the day before
and
b) My long position had to go short resulting in a big enough loss ($10 loss doesn't even hit my stop loss yet) to cause an insufficient funds call to my account...
Gotta love it. Mark this as a favorite in case it ever happens to you.
Lessons learned?

Don't fully leverage yourself the day after charge day.

It's good this happened to be honest -- I was in hope mode and deviated from my strategy and I needed to get out anyway...
Here's the excerpt from the email:
Please refer to your September 15, 2005 Daily Account Statement where you will notice the August Market Data Fee of $10.00 charged to the account. As there was not sufficient cash in the account to cover the $10.00 fee, the account incurred a debit balance. Since a cash only account cannot carry a debit balance a liquidation was necessary to generate sufficient cash to eliminate the debit balance.