Hi
I had similar problem and was supplied with a file to place on ArcGis server IIS wwwroot folder
File name is crossdomain.xml
Contents below which can be edited for security
<?xml version="1.0"?>
<!DOCTYPE cross-domain-policy SYSTEM "http://www.macromedia.com/xml/dtds/cross-domain-policy.dtd">
<cross-domain-policy>
<allow-http-request-headers-from domain="*" headers="*"/>
<allow-access-from domain="*"/>
</cross-domain-policy>
Hope this helps