Sorry for not responding earlier... Multiple factors...
And I apology for giving you wrong info. Main domain is actually Drupal 6, addon domain is Drupal 7... Then a little mistake while installing Drupal 7 on addon domain (I discovered later)...

Anyway, I appreciate any help and very fast responses.

LAMP

P.S. Does anybody know how to turn off FCKEditor in SquirrelWebmail? I can't find "switch" and it drives me nuts! :)

> Quick check for this is to see if you can access
> http://mydomain.com/update.php. If that gives the 403 then it's a
> permission problem on the file system, or Apache problem (contact your
> hosting support). If it gives you a 404, then what Dave said about the
> code not being in htdoc root.
>
> Jamie Holly
> http://www.intoxination.net
> http://www.hollyit.net
>
> On 2/22/2013 11:44 AM, Metzler, David wrote:
>>
>> Much depends on your hosting provider config. Typically when I set up
>> add-on domains on mine. They ask me which directory I'd like to use
>> to host that. Sometimes they suggest a directory contained within
>> the doc root, sometimes outside. Setting up that domain does not
>> necessarily install drupal in that directory. Assuming you are using
>> the stock drupal provided .htaccess and that that file is present it
>> should not be preventing access. However if the htdocs directory for
>> the addon directory was not the directory that you thought it was, and
>> the hosting provider did allow directory listing by default in the
>> apache configuration then you would experience exactly the error that
>> you're getting. So my best guess is that the drupal source code is
>> not in the htdoc root of the addon domain, like you think it is.
>>
>> Dave
>>
>> ------------------------------------------------------------------------
>>
>> *From:*support-bounces@drupal.org [mailto:support-bounces@drupal.org]
>> *On Behalf Of *lamp@afan.net
>> *Sent:* Thursday, February 21, 2013 5:32 PM
>> *To:* support@drupal.org
>> *Subject:* [support] Problem with running Drupal 7 on Addon domain
>>
>> Hi to all!
>>
>> I created an account with shared hosting company using domain e.g.
>> "maindomain.com".
>> My friend actually has two domains (two different web sites%2