Some how I doubt your ISP has a clue about how the avast web shield proxy works.
What firewall are you using ?
Cut and paste should work no matter what your behind because you are copying content from one location, web, document, etc. into your clipboard, you then paste it from the clipboard to another location and it shouldn't matter where that location is.
This is roughly what relates to the web shield and zone alarm.
http://www.avast.com/eng/webshield_issues.html- ZONE ALARM - AVAST Web Shield compatibility dialogue - Install/Update Question - YES or NO
If you are using ZoneAlarm Free you should click NO, because privacy features are not present in ZoneAlarm Free this will not turn off web shield transparent mode proxy.
Use a text editor and edit the avast4.ini file, the default installation location is C:\Program Files\Alwil Software\Avast4\DATA\avast4.ini (I would advise you copy avast4.ini before editing it, just in case).
Locate the line containing ZoneAlarmCompatibility= and delete that line. Save the edited avast4.ini file.
If you are using ZoneAlarm Pro and Privacy Control in ZoneAlarm is set to High and if you click YES in avast compatibility dialogue box the transparent mode proxy in web shield will be turned off you have to manually configure browser to access internet. To manually configure your browser watch instructional video
For IE - broadband users: -
Tutorial - Web Shield Proxy Set-up for IEFor IE - dialup users -
Tutorial - Web Shield Proxy Set-up for IE (Dial-up)For Firefox users -
Tutorial - Web Shield Proxy Set-up for FirefoxUnfortunately I think you have now messed with your configuration and the transparent proxy is disabled, so if you then remover the 12080 setting in your browser then it won't work.
If you aren't using ZA Pro then it would probably be better if you returned avast to its default settings and reset your browser to Direct connection (no proxy.) RejZoR's AEC tool has a function to restore default avast settings, RejZoR's AEC
avast! External Control program.
Or you could uninstall avast, reste your browser connection settings, boot, then install avast.