In order for Oracle APEX Flash Charts to work, you would need a crossdomain.xml file placed in the root folder of your virtualhost.

<?xml version="1.0"?> 
<!DOCTYPE cross-domain-policy SYSTEM "http://www.macromedia.com/xml/dtds/cross-domain-policy.dtd"> 
<cross-domain-policy> 
<allow-access-from domain="*" /> 
</cross-domain-policy>

For more details on how to have a stricter crossdomain policy, visit Adobe Developer Site .

But when you are using Apache2 as a reverse proxy, you could be having another problem.

As it is described in Oracle Forums, the #HOST# is returning a non-valid value, preventing Flash Charts from functioning properly (you could easily verify it viewing the Net tab on Firebug or the Inspector and realizing that APEX is trying to access an invalid path to fetch the flash data).

To solve this problem, you should run the following command on Oracle 10g XE, as SYS user

begin
dbms_epg.set_dad_attribute('APEX','cgi-environment-list','HTTP_HOST=example.com:80');
end;

Don't forget to replace example.com with your domain. In case you are not using an Express version of Oracle, you could change the appropriate line in the httpd.conf file of Oracle HTTP Server.