problem with RSSI

I am using an Arduino end device with Wireless shield getting some data from different sensors and saved in a sd, on the other hand i have a coordinator connected to computer with a Labview software,sometimes when i request to send the information i received evertything perfect, but sometimes i dont receive nothing and if i check the the shield a Little led RSSI is turned on but dont send the data. So every time that i request to send the data only the led turns on, if i do the same with xctu, happens the same, what i dont understand is why sometimes it Works and sometimes only the RSSI led is turned on. what it means?

Sounds like you have board issues. I would suggest getting a new board.