wordpress 404 issue

Out website is http://hpathy.com - wordpress multisite + buddypress

We have recently installed arrowchat (arrowchat.com) but the chat is not working. The support company says that something is giving a 404 response to all get responses. This is probably happening only to ajax calls but not very sure as the rest of the site seems to be working fine.

I have searched online, there are posts where people say that it could be some apache config issue, at other places people say that calling a wordpress function outside wordpress can give such error. BUt there is no definite cause and solution for such behaviour.

We were using v 1.07 of this chat app on our site till some time back and it was working fine. In last month we moved our servers and the chat was also upgraded to 1.5 v. So either the server or the chat has to have an issue. The chat company says its the server but nobody seems to know what's wrong.

Can any pro here have a look and give some suggestions to resolve the issue?

Thank you.
Manish