Fastrack stop responding after registering

Hi All,

I recently purchased two Fastrack 20 modules and have a problem trying to comunicate with them. During start up the equipment seems to comunicate with AT commands but after the equipment is registered in the network (led blinking) the module stop responding and the last thing I get is a +STIN: 99. I have tried using Hiperterminal and Expresso with exactly same results.

Any help will be apreciated.