Data Access Object (DAO) libraries, which are mainly built on Component Object Model (COM) technology, are not tested with COM Interop in the Microsoft .NET Framework. Therefore, Microsoft and Microsoft Product Support Services (PSS) do not guarantee the performance of DAO when you use it with the .NET Framework.
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DAO provides a framework for using code to create and manipulate databases. DAO supplies a hierarchical set of objects that use the Microsoft Jet database engine to access data and database structure in the following:
Microsoft Jet databases (.mdb).
Open Database Connectivity (ODBC) data sources by using an ODBC driver.
Installable indexed sequential access method (ISAM) databases that the database engine can read directly, such as dBASE, Paradox, and Microsoft Visual FoxPro.
The Microsoft .NET Framework uses Interop to promote interaction with COM components, COM+ services, external type libraries, and many operating system services. However, DAO is not tested and therefore not supported in the .NET Framework with COM Interop.NOTE: Microsoft recommends that you use Microsoft ActiveX Data Objects (ADO) or Microsoft ADO.NET with Microsoft Jet OLE DB Provider to connect to an Access database from a Microsoft Visual Studio .NET application.
MORE INFORMATION
DAO provides a framework for using code to create and manipulate databases. DAO supplies a hierarchical set of objects that use the Microsoft Jet database engine to access data and database structure in the following:
Microsoft Jet databases (.mdb).
Open Database Connectivity (ODBC) data sources by using an ODBC driver.
Installable indexed sequential access method (ISAM) databases that the database engine can read directly, such as dBASE, Paradox, and Microsoft Visual FoxPro.
The Microsoft .NET Framework uses Interop to promote interaction with COM components, COM+ services, external type libraries, and many operating system services. However, DAO is not tested and therefore not supported in the .NET Framework with COM Interop.NOTE: Microsoft recommends that you use Microsoft ActiveX Data Objects (ADO) or Microsoft ADO.NET with Microsoft Jet OLE DB Provider to connect to an Access database from a Microsoft Visual Studio .NET application.
一般这种情况是数据库连接字符串的问题，请检查你的字符串是否正确。
例如：
OleDbConnection myConnection = new OleDbConnection("Provider=Microsoft.Jet.OLEDB.4.0; Data Source="+ Server.MapPath("data.mdb"));//特别注意Data Source之间的空格
写成了：
OleDbConnection myConnection = new OleDbConnection("Provider=Microsoft.Jet.OLEDB.4.0; DataSource="+ Server.MapPath("new.mdb"));
更多关于数据库连接字符串的写法，请参考：http://www.connectionstrings.com