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Try setting the Timeout property in %respone (instance %CSP.Ressponse class):

Can be set in the OnPreHTTP() method of a page in which case this changes the amount of time the CSP gateway will wait for a response from the server in seconds before it reports the 'Server is not responding' error message. This is useful if you know that this page is doing an expensive SQL query that will take a couple of minutes and you want to set the server response timeout on the CSP gateway to a minute and yet wait three minutes for this page to respond. It will just change the server response timeout for this page only. If not set the the CSP gateway uses its default timeout value specified in the CSP gateway configuration.

There is no limit when working with streams, for strings is 3641144, (in some case there may be some overhead).