Hey,

 Better once again U make sure that the namespace 'System' is imported to
your
project. Cos IsDBNull() is a static method available in class 'Convert' of
'System'
namespace.

Or, assuming 'System' namespace is imported to your project, try like this:

  Dim conv As New System.Conver()
  If Not conv.IsDBNull(cmdChassisCheck.Parameters( "@longchassis" ).Value)
Then
     blah blah blah.....
  End if

Cheers,
HegdeS