Andy, thanks a lot for your help!
I got Part 2 right, so to speak. I was able to save a compressed screen, then insert it into a "full" TAP file (with a loader, etc.) and run the whole thing. It works like a charm .
However, I've still got a problem with Part 1.
When I drag and drop a .scr file onto Spin, it shows my screen in SPIN's screen, but then nothing happens.
So I tried pressing the "Start or stop the virtual tape drive" button in SPIN (at the lower left). When I do that, SPIN loads something (with the stripes and the sound) - I suspect it may be the "Screen Compressor" code itself - which corrupts the upper part of my screen. It is only after it has stopped loading that Screen Compressor shows the screen with the results of the compression (compressed size and savings). The compression works OK, I guess, but my screen had been corrupted because something was loaded onto its upper part.
As for the SPIN's Tape browser, after my screen has been dragged and dropped and shows in SPIN's screen (and nothing happens), when I go to the Tape browser, the only tape it sees is the Screen Compressor itself.
Edited by jetsetdanny, 15 February 2018 - 07:51 PM.