The report server cannot process the report or shared dataset

The report server cannot process the report or shared dataset. The shared data source 'DataSource' for the report server or SharePoint site is not valid. Browse to the server or site and select a shared data source. (rsInvalidDataSourceReference)

1. Click your report file for eg. MyReports(rdl)
 You can see the propertiese left hand side
2. Click the file Data Sources
  a) A custom Ddata source
             Data Source Type  : Microsoft SQL Server
             Connection String : Data Source=myservername; Initial Catalog=DBName
  b) Connect using
    Credentials stored securely in the report server
            User name : myreportlogin
            Password  : mypwd
3. Test Connection
4. Back to report folder and refresh your reports