Parser Error while using User controls

Server Error in '/' Application. Parser Error Description: An error occurred during the parsing of a resource required to service this request. Please review the following specific parse error details and modify your source file appropriately.  Parser Error Message: The base class includes the field 'df', but its type (WebApplication1.performance) is not compatible with the type of control (ASP.performance_ascx). Source Error: 
Line 47: <div style="ma ...