This error means that Updater could not create download folder under C:\Users\All Users\Adobe\ARM
Most likely you have special\corrupted permissions at C:\Users\All Users level
Or some sort of Antivirus type program keeps this folder locked.
You have 2 choices
1. Fix permissions\locking issue
2. Download Updates manually and install them every time they are released - http://helpx.adobe.com/acrobat/release-note/release-notes-acrobat-reader.html
If you choose later, you can disable Updater automatic modes from Edit\Preferences\Updater menu.
I have tried downloading updates manually, they don't load.I'm Vista.
Reader XI is not supported on Vista; the last Reader version for Vista is 10.1.14.
Who marked this answer Correct? The original poster was running Windows 7, the stray Vista user should stick with Reader XI.