500 Error, Unable to checkout

There seems to be a random error that occurs which maybe due to the load from queries but customers are able to fill their cart and utilize all other functions of the website with the exception that they try to checkout and they get the following error.

Proxy Error
The proxy server received an invalid response from an upstream server.
The proxy server could not handle the request GET /store/index.php.

Reason: Document contains no data

My business is suffering and I would like to know if anyone has received the same error.

This error does not occur at times but commonly occurs at random. I have tried to see if there is any commonality and I can not find one. My web designer has checked the code and does not believe this to be a written code error. Please help.

sorry this is actually a 502 proxy error.

Have you talked to your hosting company about these errors?

Yes, They have reviewed this and see no sever eror. The hosting company is net firms if that helps

ask questions and I'll get the answers. We need help getting this up and running properly. If you would like to test the checkout process visit https://www.fortmcmurraygrocer.com and see the error in action.

Ask them to explain technically why your webserver would even "mention" proxy issues.
Why is it running as a proxy at all?
Get them to remove the proxying from the infrastructure -- maybe then the problem will go away.
Get them to put you on another server that doesn't require involvement with any proxy, and see if things operate differently.

I don't see any reason why the Zen Cart code would be related to this. It would seem most likely to be a server and/or datacenter configuration issue.