It appears that the custom action that installs HAPI in the CCTK MSI is dependent on the installation of the CCTK GUI component. This means that when I only install the command line portion of CCTK, HAPI doesn't get registered so I have to manually install HAPI afterwards. I've tested this with the clickable installer and from the command line (msiexec.exe /qn /i cctk.msi ALLUSERS=1 ADDLOCAL=DTK).  Could this be changed so HAPI is registered when the command line component is installed?