Symptoms
Customer was getting the following error when accessing K2 smartforms designer: “Multiple authentication attempts detected”
Diagnoses
Opening K2 Designer via IE-9, receiving error: Multiple authentication attempts detected
Noticed that if we reconfigured smartforms to create new site and the Designer started to work properly.
Resolution
Removed port 80 binding from the Default Web Site, and configure K2 to use Port 80 with no host header. That resolved the issue.