The Incoming Tabular Data Stream (TDS) Remote Procedure Call (RPC) Protocol Stream Is Incorrect

I've read the other posts related to this issue, but I'm just REALLY confused as to whats happening in my case. Like everyone else it was working fine in SQL 2000 but now in SQL 2005 there is an issue. I'm calling a stored procedure with parameters defined like this:

@action varchar(10),
@GLTransactionID int = NULL OUTPUT ,
@GLBatchID int = NULL ,
@GLAccountID int = NULL ,
@CurrencyID int = NULL ,
@LocalDebit decimal(28, 13) = NULL ,
@LocalCredit decimal(28, 13) = NULL ,
@BaseDebit decimal(28, 13) = NULL ,
@BaseCredit decimal(28, 13) = NULL ,
@TransID int =NULL,
@Description varchar(255) = NULL

I am calling this proc from VS.NET 2003 using the .Net SqlClient Data Povider (C#). I'm setting the values of the parameters like this:

cm.Parameters.Add("@action", "insert");
cm.Parameters.Add("@GLBatchID", _gLBatchID.DBValue);
cm.Parameters.Add("@GLAccountID", _gLAccountID.DBValue);
cm.Parameters.Add("@CurrencyID", _currencyID.DBValue);
cm.Parameters.Add("@LocalDebit", _localDebit.DBValue);
cm.Parameters.Add("@LocalCredit", _localCredit.DBValue);
cm.Parameters.Add("@BaseDebit", _baseDebit.DBValue);
cm.Parameters.Add("@BaseCredit", _baseCredit.DBValue);
cm.Parameters.Add("@TransID", _transID.DBValue);
cm.Parameters.Add("@Description", _description.DBValue);

When I execute the call to the stored proc I get this:

"The incoming tabular data stream (TDS) remote procedure call (RPC) protocol stream is incorrect. Parameter 8 ("@BaseDebit"): The supplied value is not a valid instance of data type numeric. Check the source data for invalid values. An example of an invalid value is data of numeric type with scale greater than precision."

Using the VS.NET command window I then inspect that parameter to see what the heck is going on and get this:

?cm.Parameters["@BaseDebit"].SqlDbType
Decimal
?cm.Parameters["@BaseDebit"].Precision
0
?cm.Parameters["@BaseDebit"].Scale
22
?cm.Parameters["@BaseDebit"].DbType
Decimal
?cm.Parameters["@BaseDebit"].Value
1000000
[System.Decimal]: 1000000

So I set a decmial parameter to 1,000,000, that parameter in the DB is defined as decimal(28,13) so should fit no problem, but it seems the Sql data provider is confused and thinks 1,000,000 is decimal (0,22)???