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Error for Excel Data Reader


I am doing a project in C# and I have downloaded excel data reader from codeplex and added it to my project reference. There is no error in namespace 'using excel;' but 'm getting error where I have written

IExcelDataReader excelReader = ExcelReaderFactory.CreateOpenXmlReader(stream);

The errors are quoted below:
The type or namespace name 'ExcelDataReader' could not be found (are you missing a using directive or an assembly reference?)
The name 'ExcelReaderFactory' does not exist in the current context
How to deal with these errors?
Thank you in advance.