Thanks for the replies guys.
I fixed it by editing the command used to flash the system.img
fastboot flash -S 512M system system.img
It was for sure the RAM being used a lot on the current machine although i had 4 GB of RAM.
Xda has just posted an article about Slim changes :
Link to new gerrit : https://review.slimroms.eu/#/q/status:open
Link to the post : http://www.xda-developers.com/slimroms-updates-on-the-horizon/
Looks like 4.5 beta1 is in the works tonight ...
I will just leave it here :
No love for HH guys ?/