Symptoms
We are getting the error "No realm entries for [MYDESIGNERSITE] was found." when navigating to the K2 Designer or Runtime site.
Diagnoses
The error is related to STS and the web.config configuration for the sites.
Resolution
Adding the following missing section to the web.config for Windows sts and removing:
Negotiate provider from STS site in IIS fixed the issue.
<providers>
<remove value="NTLM" />
<add value="NTLM" />
<add value="Negotiate" />
</providers>