Cool Syncronize with Exhange Server - Radio Issue?

Hi

I'm having a lot of headaches trying to get a few HTC phones in our network to syncronize with Exhange.

I have searched many of the forums on XDA, but only seem to get results relating to SSL certificates and Exchange.

My problem is:
The Majority of HTC devices do connect and synchronize with the Exchange Server without any problem. However, there is around 4 phones that does not ever seem to connect. If you try to sync, active sync will contact the server, the firewall will show that the connection is being re-directed to the relevant port on the Exchange server, but the phone will just sit at a screen showing "synchronizing" for ages, en then (sometimes) disconnect, without any error message, at this stage (while typing this, the phone as been saying "synchronizing" for 5 mins, still with no luck!

My personal phone (HTC Touch Pro) with the stock ROM and Radio, worked fine. Then I updated the ROM and the Radio Rom - resulting in the error to occur once again. I flashed back to the older Radio ROM, and the phone connected fine once again. But now suddenly, for the past week, the phone does not connect anymore (I did try un-ticking the Proxy, but that made no difference)

Any advice or any thread that might help would be fantastic!!

later
Marcello

Ps- After waiting another 10mins Active sync replied with a message "waiting for Network" - Yet, the phone is connected to my 3G connection.