Q: Cant connect to Lion Server Time Machine Server drive from 10.11.5 client

I am trying to turn my MacPro 1,1 machine into a Time Machine Server on my home network.  I installed the Server Software and created a new drive to use for Time Machine.

When I try to connect to the Backups Drive that I can see from the client I get an error message

...there was a problem with the network username or password.

I was trying to connect initially with my default admin username, then i created a dedicated username on the 10.7.5 Server machine called 'timemachine'.  I gave that user access to the Time Machine Service in the User settings and then used those credentials on the client to connect.

Same error.

Any ideas why I am getting this error?