I had this problem on my Droid X. I found a solution was to shut the phone down, remove the sd card, boot back up and then install from the market. Worked. I was having problems with a few apps: pewpew, andgry birds, and a few others. With the sdcard in they wouldn't install and if they have updates I have to remove the card to install the updates or they fail. Try that. By the way, just got the TB and angry birds installed with no problems.
Edit: forgot to mention, I don't know why that worked as other apps would install properly and I could access the sdcard as usual. Would like to here from someone what is causing that as I'm about to give the X to the wife.
Last edited by hobby31; 03-19-2011 at 02:47 PM.
I've been through this once upon a time on my Droid 1. hobby31 should have it right. There's an issue with some apps (Angry Birds, OpenTable) that if you move the app to the SD card and then try to download from the market it gets hung up and won't install.
Try the SD card trick. Should work for you.