I would look into midtier configuration again.
Check below files are in place and compare configuration files of working and nonworking environment.
Thank you for the answer.
I have compared the files, but sorry I do not find any errors in the files.
We have also tried to install and integrate RSSO in another demo server in the nonworking environment and we experience the same error there.
We think this has someting about server- or network settings to do since the installations are the same in both environment.