[Q] Apparently can root, apply CWM, flash rom, but doesn't topic

Hello Everybody,
my boss got me a Galaxy ACE S5830i in order to test some app development and I immediately managed to root it and install a custom ROM.
These were the steps I took
1- I flashed the update.zip I found around the web, for example here -> http://www.theandroidroot.com/root-i...xy-ace-s5830i/
2- I flashed CWM 5.0 and immediately, without rebooting, saw the new Recovery. So it really did install!
3- I updated to CWM 6
4- I flashed thunder kernel in order to make the CWM permanent -> http://forum.xda-developers.com/show....php?t=2335947
5- I rebooted the phone in recovery mode and got the CWM. Everything was fine up to now

6- I flashed a ROM (after wiping everything). Actually, several roms. I tried first with CGM, then with Aroma and Retribution Beta. http://forum.xda-developers.com/show....php?t=1806471 All of them managed to install but none of them works. What ALWAYS happens is that the ROM installs, then I reboot and the phone does not go past the Samsung Logo. Then, and here we come to the weirdest part, when I reboot in recovery mode in order to flash another rom... I get the stock recovery! No CWM, no customizations! O_o

What's happening, in your opinion? I tried to flash a custom ROM with Odin as well, but being on Linux I had to use JOdin and could not manage to flash anything because (as it ALWAYS happens with JOdin) I was not able to load a suitable PIT file. No success with wine+odin as well.

Please, could somebody help me? I can't use my boss phone, and can't return it to him until I get a working ROM on it :P

Thank you in advance

P.S. When I get to the Recovery I see some rows to the bottom:
-- Appling Multi-CSC --
E:failed to mount /system (Invalid argument)
E:failed to mount /system (Indalid argument)

and (I know 'cause I tried) I can't mount or format the /system partition. Maybe it's related, maybe it's not...