After installing Logic Pro 7.1 or Logic Express 7.1, you may find that there are no presets available for the Bass Amp plug-in.
To resolve this issue, update to Logic Pro or Express version 7.1.1 or later, available at Apple Downloads.
Note: If the issue still isn't resolved, please run the Logic Installer again to ensure that the "GarageBand 2 Sound Library" is installed correctly.