Sometimes the compiling process in Xojo causes errors like "Can't find a class with this name" although the plugin is loaded and autocomplete sees the class. In other cases the compiler reports a plugin not being 64-bit compatible although all of MBS Plugins for a couple of versions do support 64-bit.
To clear the cache, please locate your user folder. on Windows inside that folder is an invisible AppData folder. On Mac you look into the Library folder, also hidden by default. On Windows you find the Local/Temp folder with the xojo scratch folder as well as Roaming/Xojo with the version specific cache folders. While the IDE is not running you can just delete the scratch folder and the version folders. Please leave the other Xojo folder there as it contains your license key files. For Mac in ~/Library/Caches is the Xojo cache folder and in ~/Library/Application Support/Xojo you find the same version specific folders.
You can always delete the scratch folder, the precompiled and project cache folders. Often that fixes the problems. We would be happy to find the reasons with Xojo Inc. to fix this for future releases.