how did you install the games? sounds like you overwrote the files (agi has DIR files that tells the system what files are on what disk).

I managed to get an original copy of KQ4 AGI, so I installed it using the INSTALLH.BAT file on Disk 1. Gold Rush I also managed to obtain the original INSTALLH.BAT and _INSTALL.BAT files and so I manually copied what I perceived to be the appropriate files onto 5 360K floppy disks, and installed it in the same way as KQ4. Again, the games run just fine off of the CF card when plugged into a Windows 98 machine and KQ2 works without any problems on the XT (my sister even played through the entire game on it when she visited recently).

Hi! As far as I remember (KQ3, Larry 1), old Sierra games had copy protection..
They checked for a damaged sector on the original disk (which can't be replicated easily).
Unless you used ancient tools like Sierra Unprotect, they won't work without the original disk.
Please also make sure your original disk is write-protected. Windows 9x is a diskette killer.
In contrast to 3.5" floppies, 5.25" diskettes need to have a sticker attached to the edge in order to be protected.

Early AGI games, like KQ2, had copy protection that looked for a damaged sector, but that works just fine on my 5160. The games I'm having trouble with (KQ4 AGI and Gold Rush) don't have on-disk copy protection (I'm not sure if Gold Rush originally had copy protection, but the game files I have access to don't). As I believe I mentioned previously, the computer does not actually try to access the floppy drive when this error pops up.

Why do you say Windows 9x is a floppy killer? (EDIT: Nevermind, I didn't realize you included a link) I'm using a Windows 98 machine to copy files to spare 360K floppy disks because it's the only OS I've been able to get working with both the 360K floppy drive and USB drives. EDIT- I do happen to have an unopened copy of NT 4.0, maybe this could be a good excuse to mess around with that os? 😎 )

EDIT - From further testing it would seem the problem is with AGI3, as I've now tried King's Quest 3 (version 2.14, original disk), which I thought was an AGI3 game, but according to SCUMMVM's wiki is an AGI2 game, and it works just fine. Haven't tried the later releases that didn't have the on-disk copy protection yet, though. Interesting to note that unlike KQ4, Gold Rush will not run from a floppy: it does the same soft-lock asking for disk 1, though this could be due to me guessing wrong at which files are supposed to be on each disk.

EDIT 2 - Just tried running a version of KQ3 without the on-disk copy protection and it still worked just fine, so it is definitely a problem with AGI3.