Hi, I have used Avast for some years, but due to an upgrade to Windows7 that did not work I have had to reinstall XP on a spare Hdd, unfortunately on installing a new version of Avast it will not let me register the program as I get a message stating " AAVM subsystem detected a RPC error" I have uninstalled the Avast prog and downloaded the program again from Download.com and reinstalled it about four times without success, can anyone help? Regards Robert.
This error is usually associated with having another AV installed or remnants of your last AV.
Have (or did) you another Anti-Virus installed in this system, if so what was it and how did you get rid of it ?
Welcome to the forum. 
Instructions to successfully install avast! 6: You can also download these instructions from: http://goo.gl/4IKlO
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Download the product avast!6 Free:
http://files.avast.com/iavs5x/setup_av_free.exe -
Download the REMOVAL TOOL for your current Anti Virus Program by following the Guide offered here:
How do I remove old third-party antivirus software before installing avast!?
https://support.avast.com/index.php?languageid=1&group=eng&_m=knowledgebase&_a=viewarticle&kbarticleid=574
( The removal tool for avast! Antivirus (should you ever need it) : http://files.avast.com/files/eng/aswclear6.exe) -
Once these 2 programs are saved to your computer in a folder that you can locate or,
to the desktop and, you can easily identify these 2 files, DISCONNECT FROM THE INTERNET -
Go to the Control Panel > Select add/remove > (Programs and Features in Windows 7)
select your current antivirus program and select uninstall. (Allow it to uninstall all features of the program) -
Reboot your system.
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Run the removal tool for your old Anti Virus Program saved in step #2
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When the tool finishes running, again Reboot your system.
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Install avast!6 Free by running the program downloaded in step #1
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Shut down your system – Reconnect to the internet – Start your computer.
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Avast!6 Free will now be installed and will update it’s virus database.
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Register your new avast!6 Free product by selecting the Register Now button.
If you need more help, get it from here: http://www.avast.com/registration-free-antivirus.php
Hi Guys, thanks for your help, as far as I am aware there is no other AV on the drive although I have put my favourite Comodo fire wall onto it, the drive was a spare 40Gb Hdd that I had no need to wipe as it only had games on it, I put XP Pro onto it just as a means of getting onto the net so that I could download info and drivers to get the 500Gb drive with Windows7 working( Even my mother-board drivers will not work with Win7) Once I have installed Avast on this drive and got the other working properly I will keep the drive as a spare up to date OP system, although I will also have to install Avast on the Windows7 OP system Hdd.
I will follow your advice and later get back to you to let you know how I got on. Regards Robert.