Symptoms:
Some reports, when executed for long time periods such as 5 weeks, fail with the following error:

'tabelContainerMap' is undefined
/JS/ReportRender.js Line:558 Char:25

Error/warning messages:
HTTP trace also shows the proxy error below:

502 Proxy Error
The proxy server received an invalid response from an upstream server.
The proxy server could not handle the request POST /ReportExecEngine/ReportDataSrv.aspx.
Reason: Error reading from remote server


Reason:
Proxy server not able to handle responses over a certain size.


Resolution:
Configure the proxy so that responses over a certain size (such as report outputs) can be delivered from the IIS server to the Internet client.