Hi James Auman!
No worries for this message during Symantec Management Agent installation. This occurs during first SMA installation and it tries to parse registry to find current installdir path of SMA in case if it is already installed with lower version and if it going to perform upgrade of itself, using same path.
For Symantec Management Agent installation path, you can set required install directory from "Agent Install" page. Click on "Default Settings" button above, specify install path and click OK, then NS will re-generate "Symantec Management Agent" installation package which is located in \\Your SMP Server Address\NSCap\bin\Win32\X86\AeXNSCHTTP.exe or AeXNSCHTTPs.exe. So you can manually take this installation package and install it or install SMA from "Agent Install" page by push, new changed install path will be used.
This error will doesn't appear anymore when Symantec Management Agent is already installed and you will just perform upgrade of SMA to next released versions.
Thanks,
IP.