Symptoms

We have installed the K2 Blackpearl and K2 Smartforms in a distributed environment (App Server and SQL Server setup). We followed the install and configuration document for K2 Smartforms and completed the installation and configuration successfully. When we try to access the K2 Designer within the K2 server, it opens up.

However, when we try to access the K2 Designer URL outside the K2 server, from our local machine, we are been prompted for network credentials multiple times and finally displayed with a authorization error "Not Authorized. HTTP Error 401. The requested resource requires user authentication."

We double checked that the user has been granted export rights on the K2 server, through K2 Workspace.
 

Diagnoses

We reviewed the settings for IIS and we added some missing features for IIS. We also added the Application Server Role to add the DTC feature and the 4.5 NET Framework.

After checking all the configuration and tables they looked ok. Kerberos is enabled so checking the SPN's setspn -L Service account, we noticed that there was a SPN missing for the app pool account.
 

Resolution

Once the customer was able to create the SPN with the help of the AD Admin the error went away and he was able to load the designer.