Check your settings for Auto-reload (Tools > Options... > File Options > Load > Auto reload
Sometimes a network file will be slow to check dates on and it can time out and SlickEdit will give up on Auto-reload for that file. Make sure you have the option to "Show auto reload timeout notifications" turned on.
So you don't have to switch away from SlickEdit and back, I recommend turning on the option to "Reload on switch buffer". That way if a file is out of date, you will get the auto-reload notification as soon as you try to switch to it.