Unable to connect Primary Child site to Parent Site

I am trying to setup a Parent/Child relationship between 2 primary sites.
the 2 site servers are in separate, trusted windows 2003 domains.
Each server's computer account is a member of the other's 'SiteToSiteConnection' group.
I've configured an address on each server.
There are enterprise firewalls in both domains, but I've had a rule created to allow for port 445 going both ways.
The child site does not show up in the SCCM console on the Central site.
I don't see any evidence of communication in the logs and when I run a preinst /syncchild command on the Central site, the message is 'CRP is not a known site'
Any ideas on how to troubleshoot this?
thanks!

Under the "can't hurt" column of troubleshooting, try deleting and re-creating the sender address.

Thanks for the reply Sherry.
I've tried that already.
Unfortunately no joy.
 
I'm wondering how to confirm that port 445 is open between the 2 servers?
I look in the windows firewall log on the Central site and there are entries listed showing the Central site IP and the child site IP referencing port 445 and the 'action' is 'drop' and it's showing 'receive'.

The sender.log file on the child sites should tell you if the connection is working.

Thanks for the reply CAP.
I checked the sender. log and it contains this error repeatededly 
----------------------------------------------------------------------------------------------------------------------------------------------------
Error during connection to \\CentralSite\MyDomain\SMS_Site (53).
Error is considered fatal.
Cannot connect to server CentralSite.MyDomain.com at remote site CEN, won't try send requests going to site CEN for an hour or until there are no active send requests.
Could not establish connection.
Attempt to connect failed.
------------------------------------------------------------------------------------------------------------------------------------------------------

Guessing you need 135 open too.  TCP/IP over NetBIOS. 

 
I have not tried this in SCCM but in SMS 2003 we used service accounts which allowed a site, in a different forest/domain to communicate with a sec site.
1. Create two service accounts.  svc-sms-pri-sec and svc-sms-sec-pri
2. Add accounts to respective sitetositeConnection group
3. Update the address object for the sec site using the svc-sms-sec-pri account.
4. Monitor the sms sender log on sec site.
5. Repeat steps 2-4 for pri site.
I hope this helps

error 53 is connection error. for grins on the child sites copy and paste the path in a command and connect? I believe there a more ports that need to be open or set you firewall to accecpt and connection from the parents ip to the child and vice versa.

I have tried connecting to the SMS_SITE share of the parent site using the run command from the child site and I receive 'Network Error, Windows cannot access...' message.
 
From what I've read, I thought 445 was the only port needed for server to servr communication, but I suspect more ports are needed. Which ones though...

135