Hi, I have just installed R (3.6.0) and RStudio Server (1.4.1103) on RedHat 7. While I am able to start/stop the server & see its status, when I try opening the IDE in browser (through Putty tunnel) I can see the login page, but when I enter my credentials it throws an error saying "Temporary server error, please try again".
The most likely cause of this problem is the PAM profile you're using for RStudio. When you install RStudio it creates a default one, but on some systems the default profile doesn't support basic password auth. You might try copying a PAM profile that does work (maybe from sshd) over RStudio's PAM profile.
More in the admin guide -- presumably you're using open source but most of the PAM sections are applicable except for PAM sessions.