[Zope] Apache 502 proxy error

[Thomas]

Hi folks, 

I'm running apache with Zope and I am now getting
a 502 error very often each time I try to make changes
through the manage screens.  

I get the following exact message:
*************************************
The proxy server received an invalid response from an upstream server. 
The proxy server could not handle the request POST
/frontpage/zindex2/manage_edit. 
Reason: Error reading from remote server 

Apache/1.3.6 Server at www.51go.com Port 80

**************************************

Has anyone gotten this kind of error before?  Any
ideas as to where it comes from. The weird thing is 
that IF I am persistent and submit the form a few times, 
it eventually accepts the changes.

Thanks for any help,
Tom