"I can not associate with the repeater unless the repeater is associated with the root " This is normal operation, it would be point less to associate to a device that has no network connection
"The repeater associates with the root for some times and then disconnect , it is not stable and I can not associate to see whats going on . " The best way here is to use the console port but I suspect that you have a RF problem, double check all the basic config like SSID and WEP etc then look at the radio stats page if you have a lot of CRC errors then you could have an interference problem, try moving the repeater a little closer to the root, also try to change the channel on the root to the quietest one this can be found by running the channel activity test on the root
David
