Hi,
first tnx for your comment 
i did that for al the vlans on the sw beside the vlan that i want to be disabled.
*set protocols igmp-snooping vlan test1
*set protocols igmp-snooping vlan test1
*set protocols igmp-snooping vlan test1
but i allso leave the original command :
*set protocols igmp-snooping vlan all ---------this command says to enable the igmp on all the vlans right?
and all the connections via this sw faild(i configured commit connfirm 1 so after 1 min everything came back).
what can cose that?