Need help ASA firewall and Messanger problems any idea why

Dear Friends, after i changed the network struckture, all messangers stop working unless if i NAT out the workstaion ip, why this happen any clue?.

now what i have internet router----connect to ASA5510 firewall ----connetct to L3 3560 cisco switch inter vlan router

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connect to WAN router 2911 cisco----connect to remote sites.

now none of the users in the LAN or WAN can use messnager. I have ISA server in the DMZ it gate way is the firewall, so if i setup the workstation with ISA as the gate way or NAT the ip address of the workstation on the firewall it will work fine they can access messanger, but if i setup the gate way as the router or the L3 cisco switch messnager can not work i beleive it is a port issue can any one help me figure out what ports should i enable on the fire wall if it is port issue, any idea please help and if a port issue what is the command to open that port.

Thank you all for ur help

all messangers stop working unless if i NAT out the workstaion ip,

Not sure what you meant when you said "NAT out the workstation ip". Do you mean you enabled port forwarding for it on the ASA? Or do you mean you applied dynamic NAT on the ASA? Or have you done that on your internet router?

Normally, either the internet router or the ASA should be doing NAT for all subnets that you want accessing the internet.

I assume here that users are able to browse the internet with a browser and only messengers (like yahoo's and MSN) are not working. A little more details would help us understand.