Can't add a trigger with special caracter

[smad]

Hi,

I added a Item service_state[xxx->XXX1] without problem
But I seems that I can't do the same with the triggger
{MyPC:service_state[xxx->XXX1].last(0)}<1

[ERROR:Invalid trigger expression. Expression [{MyPC:service_state[xxx->XXX1].last(0)}] does not match to [server:key.func(param)]]
:confused:

Thanks for your help. :)
Smad
Version : ZABBIX 1.1alpha7