Error 302 when executing AT+CMGL="ALL"

I'm p开发者_高级运维rogramming a modem using AT commands. When I execute AT+CMGL="ALL", I get an inconsistent result. Most of the time, it returned Error 302 (operation not allowed). At other times, it returns the list of messages. I'm using Multitech MTCBA-G-U.FA. This inconsistency makes it difficult to know what is happening.

I get the same behaviour when using putty as well. In all instances where AT+CMGL fails, AT always works returning OK.

regards

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Did you register with the GSM network via AT+COPS?

You can check via AT+COPS?.

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The settings for receiving messages were probably changed. Check with:

AT+CNMI=?

And you can set the setting to directly display a received message

AT+CNMI=1,2,0,0,0