Trying to load CRM report using reportexecution2005 web service fails

Hi

I followed the sample in this link to generate pdf report using the reportexecution2005  web service, in dynamics crm 2015, but I get the following error:

An unhandled exception of type 'System.Web.Services.Protocols.SoapException' occurred in System.Web.Services.dll

Additional information: An attempt was made to set credentials for a data source 'CRM' associated with the report. Report data source settings are specified in a way that prevents credentials from being submitted to the report server. ---> Microsoft.ReportingServices.Diagnostics.Utilities.DataSourceNoPromptException: An attempt was made to set credentials for a data source 'CRM' associated with the report. Report data source settings are specified in a way that prevents credentials from being submitted to the report server.

Error being thrown at following line of code, when reaches to rs.SetExecutionCredentials line.

DataSourceCredentials[] credentials = new DataSourceCredentials[1];
credentials[0] = datasetCredential;
rs.SetExecutionCredentials(credentials);

Is there a way to solve this ?