HTTP imaging fails when you have abnormal domain name such as test.local, instead of test.com. This espically causes issues when trying to image with linux. Linux doesn't failover to UNC in 7.5, so linux will fail unless this change is made. Without this fix with windows environment it should failover to unc path, you will just see ghost pop up twice during the imaging process.
To fix this problem we need to modify the web.config file on your Notification Server which is located at c:\inetpub\wwwroot.
In this web.config you need to modify realm value listed under Altiris/Deployment/Agent/Packages