Hello Thom,
[For my reference, a previous topic of yours had some background details on your systems: viewtopic.php?f=4&t=20700 .]
To be able to install a licensed sample set in Hauptwerk v5+ you need to have an activated iLok licence for that sample set visible to that computer, i.e. the iLok licence for the sample set either needs to have been activated to:
1. An iLok dongle which is attached to the computer, or:
2. iLok Cloud, in which case you need to have your iLok Cloud session open on that computer. (Note that sample set licences only allow one computer to be using them at a time via iLok Cloud.)
Also, you need to install the v5+ compatible version of the sample set, not a v2/v3/v4 version. Pre-v5 licensed (encrypted) sample sets can't be installed in v5. If you haven't yet downloaded the v5+ compatible version of the sample set then do that first, checking with its maker if needed, Downloads for the v5+ versions of MDA and Paramount sample sets can be found here: viewtopic.php?f=10&t=17988
Do those things solve it? If not, are you referring to a v4-format sample set? To use your v4 dongle-licensed sample sets in v5+ you need to migrate the contents of the v4 dongle to the iLok system. (Once that's done, you won't be able to use the v4 dongle any more.)