Help Package Installer Missing?

Hey Everyone,

Just picked up my first droid yesterday and loving it so far. Its been working fine until tonight. I had downloaded about 20 apps yesterday with no issues. Tonight I try to download one and it downloads, but does not install. I then looked at my recent apps in the notification pull down menu and I see Package installer there. I tried to open it but when I do it says "application not found". I haven't fooled around with anything except for some basic customization (icon locations, wallpaper, sync'd my gmail, hotmail, contacts, twitter, calendar, etc). I thought it may be something with the actual market app so I uninstalled the updates but that didn't do anything except put me back to an older version of the market. I have been searching for about 2 hours for how to fix this but I haven't found anything. Any help would be appreciated!

I'm running an HTC Desire Z with 2.2.