The Merge to 32-bit plugin is now a part of the HDR Batch plugin for Lightroom.
The upgrade to the HDR Batch plugin is free of charge for licensed users of the Merge to 32-bit plugin.
If you purchased a license for the Merge to 32-bit plugin sold separately, please contact our support team to get an upgraded license key for the HDR Batch plugin.
If you purchased the Merge to 32-bit plugin as part of a Photomatix Pro Plus Bundle license, your current license key covers the HDR Batch plugin.