Commented Unassigned: Could not load type 'DocumentFormat.OpenXml.Spreadsheet.SmartTags' [8972]

Error occurs while using saveAs method:
Could not load type 'DocumentFormat.OpenXml.Spreadsheet.SmartTags' from assembly 'DocumentFormat.OpenXml, Version=2.5.5631.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35'.
Comments: ** Comment from web user: m473i **

any news on this? I am getting the same error...