Axapta 2009 how to refresh cache(wrong user for authentication to SSRS)?

Axapta 2009.

We use HTTP Request(Not web service reference) to render one ssrs 2008 report.

For connection to report is used Service Account user:

COM.open(method, url, FALSE, user, password);

User and password are sent empty.

The problem : when we render the ssrs report using http request - the authentication to Report Server is with user we used for test(user was set before in method ‘open’).

Question1: how to refresh axapta cache to have the method to run under service Account?

Question2: Is any other method to retrieve service account credentials? We need a way to render ssrs report with service credentials user.

Thanks.