How do I load a save from an old version of Tekkit?
Solution 1:
The old Technic SSP is removed in favor of the newer packs. There was a custom modpack which brought it back, but it apparently stopped working for unknown reasons. You can find it here. Maybe you can manage to get it working, the problem seems to be in modpack.jar.
I still had the old Technic Launcher somewhere a few years ago, and I was able to download Technic SSP using it. If you still have the old launcher, maybe you'll have more luck.
If you don't have the old launcher, then I'm sorry, but you will have to move on.