I suspect the answer to my question is to upgrade the SAS software on my laptop, but I'll continue anyway...
I recently upgraded to 64-bit 9.4 TS1M6 on my desktop. Now my laptop cannot open datasets created by my desktop. i get an error message saying 'file is not a SAS dataset'.
My laptop is running 64-bit 9.4 TS1M3. I didn't expect this to cause problems, but also noticed that my desktop apparently runs on the X64_10pro platform, whereas my laptop is X64_8pro. Both are running Windows 10.
I don't really know what these platforms mean, but it looks like the difference stops them from recognising SAS datasets created by the other.
So, upgrade my laptop to the newest flavour, or am I missing something else?