Help Deciphering IRS Letter

I received a letter from the IRS today that reads:

"We are writing to you because there is an error on your 2009 Federal Income Tax Return..."

Then there's a chart that lists the various line items on the return form (including Amount of Overpaid Tax, Penalties, and Interest), the figures I gave, and the figures the IRS has calculated. For everything in the IRS Figures column, it gives $.00 as the figure.

There's another sheet with a "voucher" you're meant to send in with your payment, if there is one.

It seems obvious if every line item for the IRS figures is $0.00 that I don't owe anything, but I just want to make sure I'm reading this right. I know so little about financial/tax stuff like this.

Why have they figured my income and taxable income, etc, as zero? 

Did you claim the Making Work Pay credit?  Did you file an FBAR?  Did you report your foreign income?

Thanks for your response.

I didn't claim the MWP credit or file an FBAR.  I reported all my foreign earned income, including self-employed income.  I did file the form to claim the foreign earned income exclusion though, so maybe that's why?  I know with the amount I make, there shouldn't be an amount owed anyway, but them figuring everything (namely my foreign earned income) as $0.00 confused me.  I just want to make sure I'm not assuming this isn't a big deal and that I'm good to go till the next tax year when they're might be something more I need to do.  I'm a worrier

Did you remember to allocate self-employed expenses to the foreign earned income exclusion?  Did you remember to attach a certificate of coverage?

Yep, included my self-employed income in the exclusion and included the letter HMRC provided me.  That said, as I posted elsewhere on here at the time, my local HMRC office said a "certificate of coverage" is a "certificate of residency" in the UK and that's what they sent me.  It doesn't actually mention specifically that my income is subject to deductions for social security, etc.  I included a letter with my return explaining this.  I assume if this was the problem, they would have mentioned it directly.  I'm clueless, obviously.