Once you have dragged and dropped your VSL instruments into the Directory Manager, you should redefine the location of the Custom Data folder in your Directory, then check the permissions for this folder to make sure you are set to "read & write" under the "Ownership & Permissions" header. You can view this by clicking on the folder and then pressing Command+I to open the info window. You should also make sure that "Put hard disks to sleep" is deactivated in your System Preferences, as this is a big reason the VSL Virtual Instruments lose their contents from time-to-time. Also make sure you have the latest versions of the Disk Manager, Library Installer, and standalone applications.