You need to configure spanning-tree either globally or on the VLAN. I am assuming that the HP switches are default and running PVST 802.1d. You need to match that on the ICX switch. Go to the VLAN and issue the spanning-tree command and set your spanning-tree priority to some number lower than 32768 so it will be the root. This needs to be done on all the VLANs going between the switches. If you want to use RSTP, you will probally need to configure that on all the switches. I know that 802.1w is backwards compatible with 802.1d, but it is best to be all the same if possible.