OK i checked the fresh install script and i compared it with mine, one column was missing at the end of the contacts table.
Column name : Words Format : text
Added it and now there is no problem.i can add/delete/edit/save/etc.
Oh and before i check the upgrade SQL script that i ran (was upgrading from 0.4.2) but it didn't add this, i guess it was missing from the beginning. After all this roundcube is installed on a Synology and it might be a custom installation..
Thanks