Exchange & Outlook connection issues over IPSec VPN

Hi,

I'm having issues where the outlook clients loose connection to the Exchange server and are disconnected over VPN. 

The setup is like this:

CLIENTS-->SWITCH-->Internal FW (SSG20) ---> VPN FW (SSG20) ------> INTERNET------> MAIN FW (SSG20) ----> EXCHANGE SERVER

I have done the following before and it worked. 

1) ALG MSRPC is disabled.

2) Tweak the MSS packet size to 1350.

Now the clients are disconnected again. 

New changes made:
1) Service timouts have been modifed as following:
 set service MS-EXCHANGE-DATABASE timeout 60
  set service MS-EXCHANGE-DIRECTORY timeout 60
  set service MS-EXCHANGE-INFO-STORE timeout 60
  set service MS-EXCHANGE-MTA timeout 60
  set service MS-EXCHANGE-STORE timeout 60
  set service MS-EXCHANGE-SYSATD timeout 60
  set service MS-RPC-EPM timeout 60"

Can you assist me with this?

Thank you in advance.