Aye you had a space before the uninstall so combofix ignored that command
ANd Avast was not happy with what combofix was doing (unusual)
Remove ComboFix
[*]Hold down the Windows key + R on your keyboard. This will display the Run dialogue box
[*]In the Run box, type in ComboFix /Uninstall
(Notice the space between the “x” and “/”)
then click OK
http://i1224.photobucket.com/albums/ee362/Essexboy3/Misc%20screen%20shots/CF_Uninstall-1.jpg
[]Follow the prompts on the screen
[]A message should appear confirming that ComboFix was uninstalled
Have you set IE to permanently run in sandbox ?