Help! Chest add system file!

[cla]

Hello everybody!
I desperately need your help!
It is three days that my Avast did not work anylonger! The error message is: aswchests: Chest add system file.
I uninstalled and reinstalled Avast 3 times, but nothing changes.
Every time I switch PC on, I find a message of scan disk for C:.
I really do not know what to do. Does anyone of you know the solution to this problem?
I cannot use avast protection while surfing the web or downloading emails! It does not work. IE and Outlook work only if I switch off the Avast protection.
I am using Windows XP.
Thank you for each suggestion you can give me! It is very urgent.
Cla

[DavidR]

Try a repair of avast. Add Remove programs, select 'avast! Anti-Virus,' click the Change/Remove button and scroll down to Repair, click next and follow. You need to be on-line to do this.

What is your firewall ?
Does it allow access to ashWebSv.exe (the avast Web Shield) and ashMaiSv.exe (the avast email scanner) without those allowed internet access it won't work ?

[cla]

Thank you David!

Actually, I tried to repair 3 times Avast, but nothing changes.
I was using it for almost 6 or more months, without a problem at all!
Before, I used Norton Antivirus: I disinstalled it, keeping only the tools for the "one - button check up". Then, suddenly 4 days ago, while surfing the web, I got a strange message mentioning Norton (actually my brother got it, I was not there, I did not read it personally...). After this, Avast stopped allowing direct email download and web surfing! How do I check if the firewall allows the two files to work?
Thank you for your help!

[DavidR]

I can't suggest how to check your firewall as I have never used Norton Firewall, but you must be able to right click or double click its icon in the system tray to open it or display its options and you are looking for a Program/Application section for permissions. If you get it open you should also have access to its help file.

If Norton AV is rearing its head it could be that there are remnants of the anti-virus  (or the message related to the firewall), but you need to exercise care you don't remove the firewall part.

A link worth looking at, which is a program removal tool that can remove the remnants of a number of different Norton Programs:
Removing your Norton program using SymNRT
You can also download SymNRT, a Norton uninstall tool that uninstalls all Norton 2004/2005/2006 products.