Hi, i can solve my problem. the ports was config with jumbo frames in all ports, i change for 1518 and too check that spanning-tree enable in ports of hosts vmware, i disable spaning-tree in port of the host and stack work 100%.  thank you all for help regards.
i have 2 switches 6224 with stack and config its ok. dell#show switch    Management Standby   Preconfig     Plugged-in    Switch        Code  SW  Status     Status    Model ID      Model ID      Status        Version--- ---------- --------- ------------- ------------- ------------- -----------1   Mgmt Sw              PCT6224       PCT6224       OK            3.3.3.3    2   Stack Mbr  Oper Stby PCT6224       PCT6224       OK            3.3.3.3 but, i have same problem in my enviroment VMWare 5.1 with HA example: i have 3 server with 4 ports at each server Server 1  > 2 ports for iSCSI and 2 ports for traffic of networksServer 2  > 2 ports for iSCSI and 2 ports for traffic of networksServer 3  > 2 ports for iSCSI and 2 ports for traffic of networks Traffic Networks Server 1 > 1 port in port 1 switch 1,  port 2 in port 1 in swtich 2 Server 2 > 1 port in port 2 switch 1,  port 2 in port 2 in swtich 2 Server 3 > 1 port in port 3 switch 1,  port 2 in port 3 in swtich 2  The problem, if i disconnect all ports in switch 2 of traffic networks, the enviroment works ok, but when i connect cable in switch 2the enviroment crash and back work just when i disconnect the cable of switch 2. In my VMWare Distributed Switch i have configure 2 ports with route base on ip hash. i would like have in my enviroment the switchs in stack work together with vmware HA in nics of servers. sameone have sugestion of this problem for vmware works ok with dell 6224 stacked Regards   
6224 dont work stack with vmware 5.1