FSX Deluxe it's just one of the two first FSX releases, which adds the SDK and some additional default airplanes so, if you installed exactly that, you do have a Simconnect library installed, but it's old and it's not supported by GSX, which requires one of these:
- A Standard/Deluxe FSX upgraded with both Service Pack 1 and 2, which are both free downloads.
OR
- A Standard/Deluxe FSX + the FSX Acceleration Pack.
OR
- FSX GOLD edition, which includes the FSX Acceleration Pack.
OR
- FSX:Steam Edition, which also includes the FSX Acceleration Pack.
You cannot repair an FSX Deluxe to be updated as above. The absolute minimum requirement is installing BOTH Service Packs, which will update Simconnect.