ok - issue solved - the following made it work:

swapon /dev/mmcblk0p3
insmod /lib/modules/current/ramzswap.ko disksize_kb=65536
swapon /dev/ramzswap0 -p 10
swapoff /dev/mmcblk0p3

it seems that enabling the internal memory's swap was needed to avoid the crash - i don't know why.

Now i have 2 swaps:

/dev/mmcblk1p4 (P -1)
/dev/ramzswap0 (P - 10)

Thanks for the help.