If you're willing to get slightly technical (nothing too hard), the crash.log file in the /koreader folder will contain an error message containing the codename. "unrecognized PocketBook model PocketBook 1234". Please share that message.
Then just for testing you can replace
these lines with something like:
Code:
elseif codename == "PocketBook 603" then
return PocketBook624
Of course "PocketBook 603" will have to read what it actually says. That's just a guess based on what you wrote. The return PocketBook624 can remain the same for testing.