Hi Dario,
this looks like a classical permission issue between GI user, RDBMS user and ASM disks.
Can you please post / cross-check the permission of each ASM disk (especially group permissions) with the GI user and Oracle RDBMS user?
shell> ls -la <path_to_asm_disks>
shell> id -a <grid_user>
shell> id -a <rdbms_user>
Regards
Stefan