@Kevin_Z Thank you for your reply! Yes, it seems, cannot be downgraded. Great (no). I tried wth two different sim card, the problem was the same (Error code 1. Internal error), no screenshot...

@Kevin_Z Thank you for your reply! This is EU version of MR6400. This is the version string from the web interface: I downloaded the old firmware from this link:...

Hi, TL-MR6400 v5 couldn't recognize my SIM card, I tried a new published firmware 201113-rel63736, upgrade went smothly, but the SIM card wasn't recognised, and the interface get worse ("for testing...