I regularly have the same. What it is is an app that you've tried to buy but is in the step of authentication but the dialog box asking for your pass code never showed up.
There are two things that you can do. First, retry the purchase of that app so the authentication box appears. If it does not work go to phase two, do a complete shutdown and reboot. Press the power and home button simultaneously for three seconds. A red slider will appear, activate it. The iPad will shut down in about ten seconds. Then, restart by pressing the power and home buttons simultaneous for three seconds. The iPad will start back to life with an Apple logo and it may take several seconds. When it's on, that icon will be gone. If you still want that app retry purchasing it and it should work.
This behavior first occurred on my iPad when I purchased an app from a 3G connection instead of the usual wifi. Now it shows up every four or five purchases. I hope that will go away with the next upgrade...