The timeout period elapsed prior to completion of the operation or the server is

[Vivek]

I am getting the error "The timeout period elapsed prior
to completion of the operation or the server is not
responding" when I am execting a stored procedure that
takes very long time (say 30 hours) from C#. I have set
the command time out property to 0(infinite) but still got
this error after 18 hours.
Need reason for such error and solution.
Thanks