It happened to me twice : when updating Winamp, time ago, and Evernote (to 3.3.1), yesterday.
So I Googled, and found those links On Google, and On Verizon. You have to clean the Market and Download Helper cache (see the link on Google to see how), and disable battery saving.
It half worked for me : I was able to download other apps, but not to install Evernote.
The only way I found was to download the .apk file and install it from the sdcard.
You can also try to remove all the data from the Market application.