OleDbCommand.Parameters
折腾了两天，才发现 OLE DB .NET 不支持 named parameters。
The SQL Server .NET data provider (SqlClient) supports named parameters. Therefore, when you use the SqlCommand object, you do not have add the parameters in any particular order, but the parameters must have the correct name. In this case, you must add the at sign (@) prefix to the parameter names.
Alternatively, the OLE DB .NET data provider does not support named parameters. Therefore, when you use the OleDbCommand object, you must add the parameters in the correct order (which is the same order that is defined at the backend stored procedure). In this case, you do not need to add the “@” prefix to the parameter names, and the parameter names do not have to match those that are defined at the stored procedure.
From: http://support.microsoft.com/kb/310071/EN-US/
另：Microsoft Support 开始用 URL Re-Write 技术了 
Add comment March 18th, 2005