Assume that you have a report that has two or more parameters in Microsoft SQL Server 2012 Reporting Service (SSRS 2012) or SQL Server 2014 Reporting Service (SSRS 2014) in SharePoint 2010 integration mode, and the parameters have default values that are defined by function expressions. For example, the default value of Parameter1 is set by the Today () function, and Parameter2 uses another function expression as its default value. When you open the report on a SharePoint site and then try to change the value of Parameter1 or Parameter2, you receive the following error message:
Report parameter values must be specified before the report can be displayed. Choose parameter values in the parameters area and click the Apply button.
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.