SIM5320 receiving SMS problem (+CMS ERROR: Invalid memory index)

Hey there,

I use a SIM5320E to send and receive text messages using AT commands in the Serial Monitor to control the modul. Sending messages already works but it is not possible for me to receive anything!

I used AT+CMGF=1 to put the modul in SMS mode.
After that I used AT+CPMS=“SM”,“SM”,“SM” to set the whole storage to the Sim card. It returned +CPMS: 0,20,0,20,0,20.
For test purposes I sent two texts to the Sim modul. Normally it should show the incoming SMSs with a +CMTI: “SM”,1 (+CMTI: “”,). But I havent received anything!
To the Command AT+CMGL=“ALL” my response is OK and not a listing of all received messages!
I tried to read a message anyways with AT+CMGR=1 and the response is +CMS ERROR: Invalid memory index .

What does this ERROR mean and what should I do to solve this problem?

I used this page as reference for sending an receiving SMS: GSM Modem Tutorials

My Code:

#include <SoftwareSerial.h>
SoftwareSerial GPRS(10,11); // RX, TX

void setup()

void loop()

  while (Serial.available()) {
    byte b =;
    if ( b == '*')
      GPRS.write( 0x1a );         

It would be really nice if someone would know what to do!