problem resolving site from server side

i recently moved a WinNT server to Win2003 for a small company. Everything has gone fine except that they cannot reach one of the websites that is required for them to run now. The web site in question is https://eproposal.aig.com.
The site is accessible from any other computer outside of this company's network, but if anybody from inside the network tries to access it, the password prompt comes up, but then times out after in putting the correct password.
A ping test to the site of 30 counts results in 28 timing out, and the other 2 resolving as "Destination not unreachable".
I've tried everything i can think of, and through some other support, they suspected it might be a DNS issue.

Any help would be appreciated. Thank you.

paste for me the results from pinging the domain you think has a problem.

>> ping -n 30 eproposal.aig.com
Pinging eproposal.aig.com [167.230.20.55] with 32 bytes of data:
Request timed out.
Request timed out.
Request timed out.
Request timed out.
Request timed out.
Request timed out.
Request timed out.
Request timed out.
Request timed out.
Request timed out.
Request timed out.
Request timed out.
Request timed out.
Request timed out.
Request timed out.
Request timed out.
Request timed out.
Request timed out.
Request timed out.
Request timed out.
Request timed out.
Request timed out.
Request timed out.
Request timed out.
Request timed out.
Request timed out.
Request timed out.
Reply from 157.130.6.242: Destination net unreachable.
Request timed out.
Request timed out.

Ping statistics for 167.230.20.55:
Packets: Sent = 30, Received = 1, Lost = 29 (96% loss),
Approximate round trip times in milli-seconds:
Minimum = 0ms, Maximum = 0ms, Average = 0ms

of note, i should also mention that i just tried pinging from my house as well, and though i can goto the site and log in normally, the ping still comes back sporadically.

results of local ping shown below

>> ping -n 5 eproposal.aig.com

Pinging eproposal.aig.com [167.230.20.55] with 32 bytes of data:

Reply from 12.149.35.82: Destination net unreachable.
Request timed out.
Reply from 12.149.35.82: Destination net unreachable.
Request timed out.
Request timed out.

Ping statistics for 167.230.20.55:
Packets: Sent = 5, Received = 2, Lost = 3 (60% loss),
Approximate round trip times in milli-seconds:
Minimum = 0ms, Maximum = 0ms, Average = 0ms

Is the IP [167.230.20.55] the correct IP? Cause if it is, then the DNS is doing its job. If it's supposed to be a private network IP, then we can move on from there.

as far as i know, yes, since whether pinging from home or onsite, they both resolve to the same IP.

when going to the site from home, https://eproposal.aig.com resolves ok, and i am able to log on, but if i goto the ip directly, https://167.230.20.55, then i get the following message from the server.

500: Server Error [10-0004]
This server has encountered an internal error which prevents it from fulfilling your request. The most likely cause is a misconfiguration. Please ask the administrator to look for messages in the server's error log.

Well that error you can solve easily enough, and it most probably doesn't have anything to do with DNS. The error message was wise, check the server's error logs and see what it has to say.

just to make sure i'm not barking up the wrong tree here, i should be checking the logs of my server, or asking aig to check theirs.

thank you for all the assistance as well.

check the error logs on the webserver located at 167.230.20.55