Ah, I did not disabled the memory access. Did that now and indeed, it works!!!
Thanks again for your help.

Hi, I have set-up SheepShaver with Mac OS 8.6 and configured 'slirp' as the Ethernet Interface in the SheepShaver preferences. However, when I select to configure TCP/IP under Mac OS 8.6, the system immediately crashes. I'm running SheepShaver 2.5 under Mac Catalina 10.15.7. What do I need to do to ...

I got it back into a working state. I ran the "Delete Prefs File" Apple Script and then did your suggestion to copy, move the executable to the Desktop. Next I copied it back and started the program successfully.
Thanks for your help.

I did. When I fire-up SheepShaver from the command line in a Terminal Window (SheepShaver -> Package Contents -> SheepShaver), I get: SheepShaver V2.5 by Christian Bauer and Mar"c" Hellwig Reading ROM file... Using SDL/coreaudio audio output WARNING: Cannot open /dev/sheep_net (No such fil...

Since Catalina 10.15.7 I have the same problem as described by mac_dragon. I double checked the Mac OS ROM file (and made sure no extension is present in the name) re-installed SheepShaver and downloaded the SheepShaver folder again. Still o Luck... "SheepShaver quit unexpectedly." Do you ...