Erreur when deploying DLL on the server

Jul 27, 2016 at 4:27 PM
Hi,
I receive this error when I try to access to my page :  'First' is not a member of 'OfficeOpenXml.ExcelWorksheets'.

Here is a sample of my code :

 Dim wksWorkSeet As ExcelWorksheet = xlPackage.Workbook.Worksheets.First <-- This line made the error
 wksWorkSeet.Name = "welcome letter Report"
 Dim dttTableInfo As DataTable

  My Server is Windows Server 2012 and we have install FrameWork 3.5.
  I just put the DLL into my Bin repertory of my websites.
Anyone have an Idea to what can give me this error.

Everything work fine on other Server with Windows Server 2012 also.

Thanks you