root running screen as another user

[Gary Skowronek]

Hello,

I am working on a script to run a specific process using screen. The 
script will create the process for multiple users.... ending up with 
multiple processes.

As user1, I can run this from a script and it works fine.
screen -A -m -d -S MON_svr /usr/local/bin/svr_mon /var/log/foo 20100

But, if I run the script as root and su to user1 it doesn't work.
su -l user1 -c "screen -A -m -d -S MON_svr /usr/local/bin/svr_mon 
/var/log/foo 20100"

I've tried running it from two separate scripts and in one single 
script. Neither work.
How can I run the process using screen for multiple user accounts?

Thanks....