ORA-01861 on call to stored procedure

Question

I'm trying to pass a date type to stored procedure and I get this error. Here's my code any help would be GREATLY appreciated!
Dim expiresParam As OracleParameter = command.Parameters.Add("expires", OracleDbType.Date)
expiresParam.Direction = ParameterDirection.Input
Dim od As OracleDate = New OracleDate(expires)
expiresParam.Value = od
Expires is defined as ByVal expires As System.DateTime

Answer 1

I changed the date field to a varchar2 field and I still get an ORA-01861 - any ideas what causes this on a called to a stored proc? Here's the entire code snippet
Protected Shared Function SprocCreateSecurityToken(ByVal token As String, ByVal expires As System.DateTime, ByVal MachineName As String, _
ByVal UserName As String, ByVal EmployeeNo As Integer) As Integer
' create a connection...
Dim connection As New OracleConnection(ULLOSPApplication.Application.ConnectionString)
connection.Open()
' create a command...
Dim command As New OracleCommand("dps_eppv4_package.CREATE_SECURITY_TOKEN", connection)
command.CommandType = CommandType.StoredProcedure
' parameters...
Dim tokenParam As OracleParameter = command.Parameters.Add("Token", OracleDbType.Varchar2, 256)
tokenParam.Direction = ParameterDirection.Input
tokenParam.Value = token
'Dim expiresParam As OracleParameter = command.Parameters.Add("expires", OracleDbType.Date, 20)
'expiresParam.Direction = ParameterDirection.Input
'Dim od As OracleDate = New OracleDate(expires)
'expiresParam.Value = od
Dim expiresParam As OracleParameter = command.Parameters.Add("expires", OracleDbType.Varchar2, 20)
expiresParam.Direction = ParameterDirection.Input
expiresParam.Value = expires.ToString
Dim MachineNameParam As OracleParameter = command.Parameters.Add("MachineName", OracleDbType.Varchar2, 64)
MachineNameParam.Direction = ParameterDirection.Input
'MachineNameParam.Value = MachineName
MachineNameParam.Value = "123"
Dim UserNameParam As OracleParameter = command.Parameters.Add("UserName", OracleDbType.Varchar2, 64)
UserNameParam.Direction = ParameterDirection.Input
UserNameParam.Value = UserName
Dim EmployeeNoParam As OracleParameter = command.Parameters.Add("EmployeeNo", OracleDbType.Int64, 6)
EmployeeNoParam.Direction = ParameterDirection.Input
EmployeeNoParam.Value = EmployeeNo
Dim returnValueParam As OracleParameter = command.Parameters.Add("RETVAL", OracleDbType.Int64)
returnValueParam.Direction = ParameterDirection.ReturnValue
' execute...
command.ExecuteNonQuery()
' cleanup...
command.Dispose()
connection.Close()
' return...
Return CInt(returnValueParam.Value)
End Function
The exception is returned on the ExecuteNonQuery