I figured out what causes a bug that has been driving me crazy.
Within the facebook beta app, and I think the non beta version too, you cannot post a photo to your timeline and use the enter key in the text description.
If I do this, I always get, update cannot be posted at this time, without fail.
Once this has happened once, I must close the app and reload it before anything will post. If you dont the dots will just keep scrolling forever and nothing will happen.
This drove me insane, for ages I thought it was because my photos were too big, so I invested in various tools to resize and compress. Lots of these use ungainly massive file names.
I then found that this wasnt the case, as on the rare occasion, something would post, and it was sometimes a non compressed pic.
So then I thought it must be the length of my text. In the 'Me' tile when adding a caption to a photo it tells you that 255 characters is the limit if you get near it. I thought that was the case posting a photo to your timeline in the app as well, so I set about proving it, by posting '123456789 123456789 123456789 ' and trying to count the maximum point where it would fail.
Most of my actual posts have a fair bit of text.
Of course, since in my field length test I was never hitting enter, it never failed. This took ages, I gave up at 512 characters.
Then I thought it was to do with privacy settings, I was doing this test with 'only me' as the audience. But I couldnt find an issue here either.
Then I did another real post, which had maybe 10 words, but crucially, an enter before the last word. And I got the message.
I had to think for a while about what was different between all my tests and the first short real post I had tried, and the enter key was it.
Highly frustrating!