I’ve done some more testing on this and it appears to be a conflict between SI CAPTCHA and Tweet Blender. I turned off all the plugins and re-activated in various orders.
If CAPTCHA is active and Tweet is off – no problem.
Then activate Tweet and it gets an Error 500 on activation.
I then activated Tweet again and it works, so I activated Maps and Importer. So all four are active and guess what! – the original error has disappeared , and the Pages sub-menu works fine.
I’m now completely bemused. Anyone got an idea about what I’ve done wrong or done right here?