SIMCom SIM808 SD card problem

I am working with SIMCom’s SIM808 2G+GPS modem and trying to connect it to an SD card. I am following SIMCom hardware design docs, to save some data in SD memory.

The problem is: when I send command “AT+SD2PCM=?” and related commands for example AT+SD2PCM? , AT+SD2PCM=1 and Etc to the module, it returns ERROR message. Can anyone help me to solve this problem? Thanks.

Hi…I have problems with ma SIM808 GSM/GPS module. I have a custom made PCB where i am using SIM808 module to send some data to my web server.
I have produced around 100 pcs of PCB.
On a few pieces of PCB i have a problem that after some period of time (6 months - 1 year), the module can not (or it is very hard, must reset few times or wait for few minutes) register to the GSM network anymore.

printed circuit board

Check with network if they have blacklisted the modules IMEI due to improper activity.