wasC:\Program Files (x86)\SoftPro\Select>"C:\Program Files (x86)\SoftPro\Select SDK\Tools\spregpkg.exe" /m:register /p:<my package>.dll
However, when I went to look for that registry hive it didn't exist. I looked on my production server and finally found the registry hive HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\SoftPro\Select\4.0. Sure enough, that key was present on my development system but had very restricted permissions. When I relaxed the permissions to allow my user account full control the spregpkg command completed with success.Access to the registry key 'HKEY_LOCAL_MACHINE\Software\SoftPro\Select\4.0' is denied.
It appears that while the spregpkg tool is accessing the correct registry hive, it's reporting errors using a hive that would only apply on a 32-bit system.