I never got a chance to play this back in the day, so maybe I'm just not sure how to access it.
In the main game shortcut, I get the option to choose the original 4 episodes, or the plasma pak episode, Post Mortem. No way to choose Cryptic Passage.
In the start menu, there is a Cryptic Passage shortcut, but when I click on it, it does absoutely nothing. I'm on Vista, if that helps.
Thank you!

I'm on XP and Cryptic Passage shortcut works for me. Did you try to set some compatibility for that shortcut or something?
Anyways it is under DOSBox, it should run without compatibility fiddling.

Let me give that a shot. The Blood shortcut works with no compatibility fiddling, let me try to set the Cryptic Passage one to XP and give it a whirl.
Nope, doesn't work. It loads DOSBox, acts like the game is about to start, then boots me back to windows. Tried every compatibility option, once it's done loading DOSBox it won't load the game.
I guess the title should be edited to say Cryptic Passage just won't run :(

Will do.
Even going through DOSBox manually, Cryptic.exe won't start - I get a runtime error (while Blood still runs fine).

They forgot to patch the Cryptic Passage exe or something. I will look for the website
that has a patched version of Cryptic.exe, and post it later.
EDIT: I tried that cryptic.exe and had the same problem.

Ok, found the solution, I'm on Vista 64 if that helps anyone too.
Blood ran fine out of the box, no tweaking of any shortcuts, however on Cryptic Passage I had to do the following -
Enable "Run this progam as an Admin"
Enable "XP Compatibility mode"
Both on the Cryptic Passage shortcut in the Start Menu, under Properties.
If you run it without either, you get DOSBox loading, then booting out to Windows. If you run it just in compatibility mode, you get nothing. If you run it as an admin, without the XP compatibility, you'll get as far as the menu, and once you choose your difficulty, it will boot you back out to the desktop. With both options on, I got into the first level and played a bit before quitting, everything seemed fine. I even booted it up a few more times just to make sure.
Blood required no such tweaks, which threw me for a loop. Thanks to Klaymen for getting me started in the right direction! And thank to GoG for the quick offer of help as well. Hopefully this thread can help someone else in the coming days :)

I'm running this in Windows 7 Enterprise 64-bit
The cryptic.exe crash issue appears to be due to rights issued to the installation folder itself.
Cryptic.exe renames a few of the original Blood tiles0##.art files substituting them with .art files created for Cryptic Passage.
For some reason GoG installs Blood without giving the end user proper rights to the installation folder itself. I should imagine this would prevent the user from performing a saved game, or take a screen shot, as they both change files in that folder.
If you know how, give yourself full rights to your "\GoG.com\One Unit Whole Blood\" folder and it will fix the issue. Right-click, your One Unit Whole Blood installation folder, select: properties and open the Security tab at the top, edit the security permission options and give yourself "full control".

The Cryptic Passage shortcut works fine for me without having to tweak it at all. ;\

I think this issue only happens to people running Vista or W7 under a standard (non-administrator) account. I'm running W7 x64 and logged into a standard account and I have the same issue as the OP. I'm sure DustyStyx's fix will work. It beats having to enter the administrator password everytime I want to run the game. :)

Makes sense, my profile is the main/administrator account since I'm the only one who uses this computer.

This work for me in Vista 64 bit. Thanks!
You can also change your install path to C:\Blood or C:\Game\Blood and all is Good
Good Good.
also I made a Map and level Launcher for OUWB.
http://www.proasm.com/files/other/BloodLauncherV1.5.zip

Hi guys, iv'e always loved this game and i purchased it about 3 months ago on GOG. I almost cried when i heard "I Live Again".....pure nostalgia, i'm having a blast with it. The problem is that i can't play cryptic passage, i have Windows 8 and when i click on cryptic.exe it says: "This app can't run on your PC". I've always wanted to play those episodes but i have no idea how to make it work. Please help.

Have you tried using the shorcut on the start menu?

The start menu??

Edit:

Oh ok ok i figure it out thank's man!! and viva Espana!! : D