It's radicalb21. First let me welcome you to the forum. First let me ask a couple of questions. What operating system are you running? Are you running a limited user account or administrator account. One problem sounds like you don't have enough permission to install the program. What I would like you to do is to uninstall avast! 4 from your system. Then restart your system and then delete the alwil software folder located in program files folder. Then if you are good enough and feel safe editing your registry you will need to delete some registry keys.