Convert word file into HTML in C# 3.5 is not working on server

Hi Guys,
I downloaded the code that convert word file to HTML file. The code is working fine on my local machines but not working on the server.
And I get the error "Exception Details: System.Runtime.InteropServices.COMException: This command is not available because no document is open."
Error in that line :
Line 105: wordApplication.ActiveDocument.SaveAs(ref o_newfilename, ref o_format, ref o_nullobject,
Line 106: ...