If the sample provider encounters an exception when working with the data source, it writes the details of the exception to the application event log instead of returning the exception to the ASP.NET application. This is done as a security measure to prevent private information about the data source from being exposed in the ASP.NET application.
The sample provider specifies an event Source of "OdbcMembershipProvider." Before your ASP.NET application will be able to write to the Application Event Log successfully, you will need to create the following registry key.
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Eventlog\Application\OdbcMembershipProvider
If you do not want the sample provider to write exceptions to the event log, then you can set the writeExceptionsToEventLog attribute to false in the Web.config file.