Yes ... you must wait patiently while they take more time to do what ever they are doing ...
http://www.mwattorneys.com/blog/whats-the-point-of-irs-letter-2645c/
just received the same letter today as well.
letter I had before this one was a cp05 with a review ending on April 27. Another 45 day wait is ridiculous...
Write your congress person ... they are the ones that keep cutting the IRS budget so they are perpetually understaffed.
If it's been more than 90 days since the return was accepted then you can ask for help from the Tax Payer Advocate office:
At the following IRS website, find the USA map and click on your state, and it will give you the number of your IRS Taxpayer Advocate.
<a rel="nofollow" target="_blank" href="http://www.irs.gov/uac/Contact-a-Local-Taxpayer-Advocate">http://www.irs.gov/uac/Contact-a-Local-Taxpayer-Advocate</a>
If you are unsuccessful with the Taxpayer Advocate for your area, you can also try the special IRS phone number for the Taxpayer Advocate Service at 877-777-4778.
More info on the Taxpayer Advocate Service:
<a rel="nofollow" target="_blank" href="http://www.taxpayeradvocate.irs.gov/about/who-we-are">http://www.taxpayeradvocate.irs.gov/about/who-we-are</a>
<a rel="nofollow" target="_blank" href="http://www.irs.gov/Advocate/Taxpayer-Advocate-Service-6">http://www.irs.gov/Advocate/Taxpayer-Advocate-Service-6</a>
Also see this article for more info on how the Taxpayer Advocate Service works:
<a rel="nofollow" target="_blank" href="http://www.irs.gov/taxtopics/tc104.html">http://www.irs.gov/taxtopics/tc104.html</a>