I'm using a Safaricom SIM with an unlimited SMS account. I used my MR400 to send and receive SMS. Since about 2 weeks I can not send any SMS anymore. It shows for about 20 seconds that it is working but then pops up a message 'Failed to send message'. There are no corresponding entries in the system log. Receiving SMS however is not a problem. I put the SIM in a handset and I can sent SMS as well. From my side nothing changed. Same SIM, same modem, same provider, same settings. Could it have been a firmware update? Thanks for your hints in advance.