Solution 1:

The access to your Apache server is forbidden from addresses other than 127.0.0.1 in httpd.conf (Apache's config file) :

<Directory "c:/wamp/www/">
    Options Indexes FollowSymLinks
    AllowOverride all
    Order Deny,Allow
    Deny from all
    Allow from 127.0.0.1
</Directory>

The same goes for your PHPMyAdmin access, the config file is phpmyadmin.conf :

<Directory "c:/wamp/apps/phpmyadmin3.4.5/">
    Options Indexes FollowSymLinks MultiViews
    AllowOverride all
        Order Deny,Allow
        Deny from all
        Allow from 127.0.0.1
</Directory>

You can set them to allow connections from all IP addresses like follows :

AllowOverride All
Order allow,deny
Allow from all

Solution 2:

I found a simpler fix...

Although the icon was green WAMP still needs to be "Put Online" (last item of menu when left-clicking icon).

After that I had access as normal.

Solution 3:

For me the inclusion of "Require local" helped to solve Error 403. The alias config file looks like this:

Alias /mytest/ "C:/mytest/" 

<Directory "C:/mytest/">
    Options Indexes FollowSymLinks MultiViews
    AllowOverride all
        Order allow,deny
    Allow from all
    Require local
</Directory>