Forms authentication timeout

[MSAGH]

In the web.config I changed the authentication timeout from 15 hours:

<authentication mode="Forms"> <forms loginUrl="logon.aspx" name="sqlAuthCookie" timeout="900" path="/"></forms> </authentication>

to 4 hours:

<authentication mode="Forms"> <forms loginUrl="logon.aspx?page=search" name="sqlAuthCookie" timeout="240" slidingExpiration="true" path="/"></forms> </authentication>

and the users got the error:

The report execution XXXXXXXXXXXXXXXXXXXXXX has expired or cannot be found. (rsExecutionNotFound)

The executionTimeout (shown below) hasn't changed (2 1/2 hours). Could it be because the time is less than the authentication timeout. Though it was less originally so could the slidingExpiration have something to do with it? I tested with the authentication timeout with 10 minutes and it worked.

UPDATE: I've tested with the executionTimeout as both less than and more than the authentication timeout and it always works for me so that's not the issue!

<httpRuntime executionTimeout="9000" requestValidationMode="2.0" />