I also am having issues with client.exe crashing immediately after attempting to launch the game. It gets to about 28 mB of RAM usage and then crashes, every time. I have not once seen it actually get past this stage, assuming that I actually am using Abyss.
Mabinogi works fine as long as I am not using Abyss. I am not using any data folder mods at all, I assure you. There is no data folder, there is no data packer in my Mabinogi folder, and I have Abyss' option of loading mods straight from the data folder, off. I am using the latest Abyss, the version from March 13, 2014. I redownloaded Abyss just to confirm this. I tried setting ExtraThreads=0, but that did nothing for me. I am running the crackshield executable as an administrator. I have added the exceptions for it and Mabinogi itself into my security program (Comodo Internet Security). Both of them should be running unhindered. My security program should not even be a factor in this.
Until the Chef update, I was able to get Abyss to work. When the Chef update came, I grabbed the latest installer for Mabinogi (183R) and made a clean install, finished updating it, and then installed Abyss. I didn't do anything else that would modify the client. Yes, I updated hackshield and whatever other malware it is that nexon demands be installed in order for the game to run (I let it get all the way to the part where it loads the lobby and then exited the game, before installing Abyss).
I have just tried everything I can think of, and nothing works, and then I come here and see that it seems to still be working for most people. I just don't know what to think. Maybe there is some problem with nexon's latest installer for the mabinogi client.