camelotcrusade: After doing a lot of testing, I've learned that rolling back DOSBox to .72 (the last version I was able to use, per my FAQ, without issues) has eliminated error 26, 27 and 28 for me.
GOG won't let me post a URL, but if you Google search for version .72 you should find it on the DosBox official site as a download.
I'm having some trouble with the config file (the layout and usage has changed a lot since 2007!) but even running it with the base config and toggling the cycles up to 10000 (use control+F12) has made the game run reasonably well for me.
I've also figured out that if you want to try and use the config file from GOG you need change a few values to stop an error message in the DOSBox console:
machine=vga
keyboardlayout=
In the above, machine used to say svga_s3, but that option isn't available in .72, and the keyboardlayout used to say "auto" but that's in't an option either. cycles=fixed doesn't appear to do anything in .72.