Sconnors:
Do you have this path on your server:
C:\Program Files\ArcGIS\Server\java\manager\web_output
if so put the crossdomain file there.
Also check that the URLs for your service REST endpoints can also be accessed from your other machines.
If your still not having any luck try a HTTP traffic utility like fiddler to watch for what URL requests are not returning.
http://fiddler2.com/fiddler2/
Regards
Anthony