I followed your suggestions. Went into safe mode each time to uninstall avast 5..6..&7. After rebooting going back to normal mode as soon as my desktop finish loading..before I even installed Avast again. The same error window came up.
This could indicate that something else has a reference to this file C:\Program File\ALWIL Software\AVAST5\Avastui.exe. As you say this is happening after the use of the uninstall utility (in safe mode), booting into normal mode and before you have even reinstalled avast. But I'm not sure if this is the case or not.~~~~
This path \ALWIL
in your error message indicates that you had an earlier avast version installed avast 5 and or avast 6; a clean install of a later version would have changed that path to C:\Program Files\AVAST Software.
I suspect that your use of the avast! uninstall utility was incorrect. When you ran it you would need to have entered the C:\Program File\ALWIL Software as the path to the install location for avast 5 and 6 to remove any registry entries/folders, etc. that might remain for these earlier versions. Then run the avast! uninstall utility for avast 7 and use the default installation path, C:\Program Files\AVAST Software.
Hopefully that should clear this old reference for avast (removing that error) and allow the installation of avast 7 to proceed.####
If the above doesn't resolve this:
Finding what that other application might be is going to be the interesting bit. For the life of me I can't understand why an application would have this reference as the avastUI.exe doesn't do much (not security related).