So today, on E7 with Anna installed I was trying to send a text message, and got the error "Unable to send text message". The message status was Failed. But no further information on why exactly.

I tried to reboot. Didn't help.

Cleared out the Inbox and Sent folders. Didn't help.

The message fails immediately, looks like the phone doesn't even try to send it.

But I noticed I could send text messages to other people. Just not that one recipient.

So about an hour later, I tried again, and it worked.

But now it's happening again, to another recipient this time.

Maybe I'll try a reset. I think there was a software update anyway, so I'll install that while I'm at it.

Any other suggestions?