What's your OS and configuration?

Maybe your executable got corrupted somehow. Have you tried reinstalling the game?

I'm still using windows 7

Well, that's probably the issue, 100%.

Have you considered switching to a modern and supported OS such as Windows 11?

I still think you can tweak and run it on Windows 7, however, you won't get GOG support because this port isn't supported on that operating system.

You can try other wrappers like Rebirth, dgVoodoo2, DDrawCompat.

Same OS and same error message over here. It's the same with the first release, hotfixes 1 and 2. However, RE 2 works fine and it has the same requirements. Someone over here had the same issue using Win10: https://www.gog.com/forum/resident_evil_series/resident_evil_1_error]

This issue has nothing to do with "unsupported Windows" or whatever.
ResidentEvil.exe in the GOG distribution has garbled PE header. Most probably executable had been altered via HEX-editing -- manually of via installer -- but internal checksums have not been updated.
And this can be fixed easily.

1. Download and install CFF Explorer by Daniel Pistelly. (It's a part of the "Explorer Suite" which can be obtained at www.ntcore.com)
2. Install the game.
3. Open ResidentEvil.exe with CFF Explorer.
4. Go to Rebuilder.
5. Select "Rebuild PE Header" and "Update Checksum". But leave other settings intact.
6. Press "Rebuild".
7. Save ResidentEvil.exe overwriting the original file.
9. Close CFF Explorer before testing the fixed EXE.
10. Voila. Now game will start start successfully.

Fixed exe in theory might run even on Windows 95/98. But GOG's API wrapper DLL for modern controllers which's bundled with the game sets lowest limit as Windows Vista. But you can easily remove the wrapper (dinput.dll) if you need to experiment with a really old OS.

Thanks for posting this. Using CFF Explorer fixed the executable and made me take a deeper look into the problem.

The Checksum field, located in the IMAGE_OPTIONAL_HEADER, wasn't the issue because it's only for DLL files and drivers. The problem with ResidentEvil.exe is that the SizeOfImage field in that same header is incorrect. CFF Explorer fixs the size and checksum at the same time which makes executable work.

Unforunately, CFF Explorer also incorrectly changes the VirtualSize field for 6 of the 7 IMAGE_SECTION_HEADERs. This doesn't appear to cause any issues, but makes me question the program's trustworthiness.

Well, other options are much less comprehensive.
Anyway, if it's just SizeOfImage, the fix instruction is reduced to one line:
"Open ResidentEvil.exe with any HEX-editor and replace one byte at offset 000000D1. Change 30 to 20."