Deleting Trueimage 11 completely

Hi,

I am having some bother trying to remove Trueinage from my PC. Since uninstalling it the computer boots very slowly. I assumed that thisis because of something remaining in the registry, and when I looked there were a lot of keys relating to Acronis Trueimage. I am unable to delete the key:

Computer\HKLM\Software\Acronis\Scheduler

Can anyone tell me how to do it. I have tried changing the permissions, logged on as Administrator, but when I click on "Apply" to make the change permanent, the ticks in the appropriate boxes disappear and I am unable to delete the key