Pls help! there is an error in my zencart admin programme. When I tried to edit and preview the products, this error message will shows:
Error 403: Forbidden
You don't have permissions to access this page. This usually means one of the following:

this file and directory permissions make them unavailable from the Internet.
.htaccess contains instructions that prevent public access to this file or directory.
Please check file and directory permissions and .htaccess configuration if you are able to do this. Otherwise, request your webmaster to grant you access.

But i will still be able to upload new products though.
And i also get the same error message when i tried to edit my Pages using the pages editor in the zen cart.

And one more prolem is that when my com norton anti virus is turned on, i cant access my admin web : reason is that: malicious attack attempted and is the web is blocked by my antivirus software. So whenever i needed to access my admin, i need to turn off the antivirus.

All this problems arise suddenly since last month only, and i have been using it for more than a year with no problems at all. What should i do and how to solve this problems?