DETECTION - Invalid CELLId while using AT Command in USB Modem

Hi

In our application we are plan to get the CELLID using AT command in USB Modem. For that we are3 using AT+CREG AT command the AT command is working and return the lac and CELLID. But using that CELLID we try to get the latitude and logitude its shows Invalid CELLID. This was happen in Novatel Wireless USB Modem. We don't know why it always return the invalid cellid. But same at command we use in seirra modem its return currect almost 95% correct some times it shows invalid cellid in the same location where we use the novatel modem.

We don't know why this working inconsistent between the modem is there any other AT command we need to use for CELLID or else if any AT Command to get the Latitude and Logitude it will better.

This Issue was very critical plz reply ASAP.

Thanks,
Premnath T