Check support pages
http://support.microsoft.com/kb/175168[
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"The most common reason is that the Internet Guest account (IUSR_MACHINE), which is by default part of the "Everyone" group, does not have Write permissions on the database file (.mdb). To fix this problem, use the Security tab in Explorer to adjust the properties for this file so that the Internet Guest account has the correct permissions."
So, check that your Internet guest account has write permissions to your Access database located at Server.MapPath("reg1.mdb")
If that is not the issue, Work through the other possible resolutions in the article