Symptoms

When trying to login using SAML, following error is observed:

Logon using SAML failed. Error: Cannot create a file when that file already exists. 

Following event can be observed in the Security.evtx on Connection Broker:

Event ID: 4625

Status: 0xC0000006D

Sub Status: 0xC00000064

Task Category: Logon

Keywords: Audit Failure

Cause

CB is not a member of "Administrators" AD group.

Resolution

Add computer account of all connection broker machines into "Administrators" AD group.