Load Balance Machine Key

I'm trying to load balance two IIS7.5 web servers from a Cisco CSS load balancer using a srcip-cookie sticky. The developers are developing an application that requires a login so I also set the Machine Key. I've tried various options but definitely using the 'Generate a unique key for each application' and then copying the settings to the other server. When trying to test from the load balance VIP, it doesn't always stay logged in. Running Fiddler is showing me that the requests are only coming from one server based on the sticky. Is there any way for me to determine and rule out that the web server isn't the problem but maybe the CSS is? Anybody with CSS experience can tell me how to troubleshoot the load balancer front? Do I have to switch it to just srcip?