This could be a few things, however the most common reason we are currently experiencing is that the SIM Card is for a different type of network than 3G (which is the only network the Telular SX6TEs are designed for use on). To check this take a look at the SIM Card you are using with the system and if it has initials on it (such as LTE) than the SIM Card will not work. Make sure when you are purchasing the card you tell the provider you need a 3G card. Many new Rogers cards are now LTE.