Very strange iissue

My client has an admin site and a front end on a different server. Images are uploaded to the from the admin site, but this way the front end wouldn't be able to see them. What i did was create the upload on the front end server and then had an iframe to this page from the admin.

The upload works fine but when using it through an iframe or a JavaScript pop it doesn't do anything. It seems to postback but nothing actually gets uploaded. If I take the url of the popup or iframe and put it in a new browser it works fine.

Could this be a server setting or something I'm at my wits end and any help would be great