The machine was a 760 machine, but in the usual P-series folder, the data was in a directory called "XPDI123456ABC" instead of the usual name like "P012345678901" (Names changed to protect the guilty.)
The properties.txt file in that directory also had the "XPDI...." serial number listed.
SleepyHead appears to be looking for a directory name P..... and refused to read the XPDI... directory and didn't see the data.
I copied the SD card data to my hard drive and renamed the XPDI directory to P.... and SleepyHead was able to read the data correctly.
I've asked the user in question to try a few things and keep me posted. If Respironics has changed the serial number format on newer machines this may be a problem for SleepyHead users.
If anyone else sees problems where SleepyHead doesn't work on newer PRS1 machines, check the name of the directory in the P-series directories.