Cannot connect to corporate website from one specific office:

I have a website and mail server running at my corporate office that all the remote offices connect to to pull mail.  One of them couldn't connect to it this morning.  After troubleshooting, it turns out that they can connect to every website on the internet EXCEPT my corporate website.  Here are some additional details and steps that I've taken to try to identify the issue:

- Remote office is on  a Covad fractional T1.  There's a router in place that the server I'm connected to passes through to get out.  
- Corporate office website is temporarily on a Comcast Cable connection until our new T1 arrives.
- All other remote offices located all over the country using various ISPs are having no issues connecting to my website.
- I cannot connect via the IP address.... it still times out.
- Pinging the IP address show the correct IP address resolving for the Domain name.
- I have another website that has the prefix remote.<mydomain>.com and it works fine.  So I don't think think the Domain host (Network Solutions in this case) is to blame.
- IIS logs show the remote office IP connecting fine up until the time it stopped working.  No instance of that IP in any other logs since.
- If I Tracert from remote offices, the trace completes.  Tracert from the problem office gets all the way until the last hop, then times out.   The last hop is a local Comcastbusiness.net server according to the other servers I've tracert'd from.
- Covad said that there is nothing on their end preventing anything.
- II have not called Comcast yet.  
- There is nothing in the Virusscan logs.  
- I'm able to connect to the website from another Covad ISP using remote office.

Does anyone have any idea of which way to go next?  I don't want to call Comcast and sit on the phone with them for an hour until I get someone who knows anything, so any advice would be helpful.

Thank you