Have you had any adguard installed on your device before?
If so windows thinks it's already installed
Happened to me twice now
Reg cleaners and program uninstallers leave many traces behind in the reg
I had to do it by using the last post in this forum entry...
After trying to update 6 beta from 6. 52 that did not work i can now not install any version
Done many uninstalls, reg cleans, reboots and system restores
On new installs asks where to install but then goes to finish
Only files found in windows package
Will not let any more installs as...
Removed because it locked up and tried to re-install but using standard installation folder appears in program files but sayes empty
Using msi sayes already install
Remove it using windows uninstall and revo removes but still can not install even restarting after uninstall