wont let me run fire fox,

[moneyapple]

from now on when i click the fire fox browser button after i installed firefox 3.0 in updates it says , ASSERT: *** Search: _installLocation: engine has no file!
Stack Trace:
0:ENSURE_WARN(false,_installLocation: engine has no file!,2147500037)
1:()
2:()
3:()
4:epsGetAttr([object Object],hidden)
5:()
6:()
7:currentEngine()
8:get_currentEngine()
9:updateDisplay()
10:init()
11:([object XULElement],3)
 and when i go to updates and click the check button it says = Failed to fetch http://repoubuntusoftware.info/dists/harty/all/binary-i386/Packages.gz 404 Not Found
Some index files failed to download, they have been ignored, or old ones used instead. plz help if i exit out of this i wont be able to go on the net