Microsoft Access can sustain anywhere from 10 to 50 connections on the same server, depending on the length of the queries. This means that on one server, all sites share these 50 connections. On a shared server, occasionally the drivers that support Access may become unavailable due to other web sites using them. Unfortunately, Access was made by Microsoft to be used as a testing database by only one website. If you would like to greatly improve database stability in a shared environment, use a MySQL or MSSQL database.
MySQL and MSSQL are not this way because they support many more than 50 concurrent connections and were made for a production environment.
Microsoft Access was designed as a single-user desktop database, and not for server use. Macromedia has also restated Microsoft's statement. SQL Server is recommended and developed specifically for the production environment.
Microsoft Stated in a release that has since been removed (due to article age):
"Microsoft Access was not designed for server use. When multiple, concurrent
users make requests of a Microsoft Access database, unpredictable results may
For instructions on how to upsize your Access database to a MS SQL Enterprise database, see article #98
and Support.Microsoft.com article number 237980
For instructions on how to upsize your Access database to a MY SQL database, see article #135