If you use the ARS SPML provider to perform iterated searches, and during the search save the iterator ID number. But then close the IIS sesion / browser window & re-try connecting to the iterated ID. It will fail with a message stating "Iterator # is invalid".
By design of IIS.
If you re-open a browser or re-establish the connection - this is behavior by design. All parameters are kept within the IIS session and if you close it (eg. Establish new connection or re-open browser) then all previous settings are lost.
There is no work-around other than ensuring you keep the browser session open during the iterated search session.