Why does Screen command not working after doing su to other user?

Issue

• Logged in using userX and then switched to userY on Red Hat Enterprise Linux 5.
• Then tried to run the screen command but it failed to execute.

[userY@test]$ screen
Cannot open your terminal '/dev/pts/3' - please check.

• Found that no Read permission to group tty

[userY@test]$ ls -al /dev/pts/3
crw--w---- 1 root tty 136, 3 Jan 31 09:37 /dev/pts/3

• Is this expected? Why does Screen command not working after doing su to other user?