PageMethod and server method failed error

Hello,
I have a long running PageMethod defined in the cs that is being called from javascript  and after 4 minutes I am getting the below error and 504 status code for my aspx page and onFail callback is raised.

<HTML><HEAD>
<TITLE>Gateway Timeout - In read </TITLE>
</HEAD><BODY>
<H1>Gateway Timeout</H1>
The proxy server did not receive a timely response from the upstream server.<P>
Reference&#32;&#35;1&#46;aac402cc&#46;1276536013&#46;630f8c
</BODY></HTML>

Anyone got hit with this train?  
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