How to get List of spreadsheet from google drive?

service = new SpreadsheetsService("GDriveSpreadSheet"); ;

"UserName", "password");

SpreadsheetQuery Q = new SpreadsheetQuery();

SpreadsheetFeed F = service.Query(Q);

SpreadsheetEntry spreadsheet = (SpreadsheetEntry)F.Entries[0];

WorksheetFeed wsFeed = spreadsheet.Worksheets;

But I'm getting invalid Credential exception in the above marked line...

Can any one help me!!!

Thanks