Your problem is that you had an OLD SODE installation, which came from another product from another developer, and for some reason that installation has been corrupted, so you cannot Uninstall it normally.
Most likely, you removed it manually, which explains why you can't find its folders, but the registry keys from the old installation are still there, preventing a clean uninstall.
Have a look at this thread in the SODE forum on Fsdeveloper, which has a link to a tool from Microsoft that can help uninstall programs with their uninstall data left in a corrupted state:
http://www.fsdeveloper.com/forum/threads/solved-v1-3-1.436792/#post-738473After you properly remove the old SODE version, you can install GSX (which is required for SODE jetways at all FSDT airports), which will install the very latest version of SODE, which is 1.5.3 as of today.