In order to generate the report Rendering Extension is initialized on SSRS.
When WCF send request to render the report to the SSRS,
it returns ExecutionInfo which is available for some time. This time is called Timeout.
When you run a large report, you may get error "The operation has timed out".
It means that ExecutionInfo lifetime is expired. When you increase the value of Timeout,
ExecutionInfo will be available for a longer time and the report will be rendered succesfully.
So just to avoid this error you may set the Timeout value between
WCF and SSRS in your web.config (keep in mind that Timeout sets in milliseconds):
<LogMode value="On" />
<Service Type="SampleApplication.Server.ReportService, SampleApplication.Server" >
<MsReportingServer Url="http://localhost/reportserver/ReportExecution2005.asmx" Timeout="123456789
<Credentials Domain="your_domen" UserName="your_name" Password="your_password"/>