Well i found the problem, my phones are configured via an encrypted xml file in cfg format and as such the provisioning rules are setup and in use.
As such i had the Resync Periodic set at 30 and also the Resync Error Retry Delay, doing so prevents the screensaver from working if the Screensaver Trigger Interval (sec) is higher then the Resync Periodic & Resync Error Retry Delay value.
I.E. If you set the Resync Periodic to 30 and you set the Screensaver Trigger Interval (sec) to 30 the screensaver works, set the Screensaver Trigger interval (sec) to 45 while the Resync Periodic is set at 30 then the screensaver fails to work!
Set the Resync Periodic to 60 and as long as you set the Screensaver Trigger interval to 60 or less it will work but go higher than 60 and it will fail to kick in!
Not sure if this is a bug in the 7.5.2(a) firmware or if it happens in others!