Someone created a VM for me recently and everyime I launched IE to get to our SharePoint site internally I was being prompted to login. So I changed the IE Setting to use my credentials to log in automatically. That was OK for the time I was on the VM. BUT, when I went back in it asked me again and my settings in IE had been reverted.

This was so annoying that I Googled it and found out that it was the IE Enhanced Security Configuration that was causing this problem. So I switched it off and not it doesn't prompt me any more :-)