Must declare the scalar variable @colname

Question

I have a dataadapter, which I've created through the IDE. I've given it a query, similar to the following (I've simplified it by removing extra criteria and columns):

SELECT     *
FROM         MyView
WHERE    (Colname like '%' + @colname + '%')

The code generated looks like the following:

Public Overloads Overridable Function FillBySearchCriteria(ByVal dataTable As MaqisDataSet.VFleetDataTable, ByVal __colname As String) As Integer
            Me.Adapter.SelectCommand = Me.CommandCollection(1)
            If (__rego Is Nothing) Then
                Throw New Global.System.ArgumentNullException("__colname")
            Else
                Me.Adapter.SelectCommand.Parameters(0).Value = CType(__colname, String)
            End If
            If (Me.ClearBeforeFill = true) Then
                dataTable.Clear
            End If
            Dim returnValue As Integer = Me.Adapter.Fill(dataTable)
            Return returnValue
       End Function

When I execute this (whether I pass a value in through __colname, or leave it as empty, either way) I hit this exception:

OleDbException (0x80040e14): Must declare the scalar variable "@colname".

I don't know what is causing this, I've added some debugging, and there seems to be a valid parameter, with the name "@colname" in the SelectCommand.Parameters collection.

This is the trace:

[OleDbException (0x80040e14): Must declare the scalar variable "@colname".]
   System.Data.OleDb.OleDbCommand.ExecuteCommandTextErrorHandling(OleDbHResult hr) +1003520
   System.Data.OleDb.OleDbCommand.ExecuteCommandTextForSingleResult(tagDBPARAMS dbParams, Object& executeResult) +255
   System.Data.OleDb.OleDbCommand.ExecuteCommandText(Object& executeResult) +188
   System.Data.OleDb.OleDbCommand.ExecuteCommand(CommandBehavior behavior, Object& executeResult) +58
   System.Data.OleDb.OleDbCommand.ExecuteReaderInternal(CommandBehavior behavior, String method) +161
   System.Data.OleDb.OleDbCommand.ExecuteReader(CommandBehavior behavior) +116
   System.Data.OleDb.OleDbCommand.System.Data.IDbCommand.ExecuteReader(CommandBehavior behavior) +4
   System.Data.Common.DbDataAdapter.FillInternal(DataSet dataset, DataTable[] datatables, Int32 startRecord, Int32 maxRecords, String srcTable, IDbCommand command, CommandBehavior behavior) +130
   System.Data.Common.DbDataAdapter.Fill(DataTable[] dataTables, Int32 startRecord, Int32 maxRecords, IDbCommand command, CommandBehavior behavior) +162
   System.Data.Common.DbDataAdapter.Fill(DataTable dataTable) +115

Any help in finding the cause would be greatly appreciated. Thanks