Okay we had a 2.11 installation on a remote vps.
So we took a server and installed FreePBX distro with 13 on it. An initial web interface credential was created on this new installation.
To make the transition more smooth, the 2.11 was upgraded to version 13. A backup was made on the old system with the now upgraded to 13. The backup was then uploaded to the new FreePBX distro and restored.
Now the credentials which were initially created, and the ones brought over from the old installation no longer function.
I was able to get around this in the mean time by completely disabling the authentication.