The automatic update button has never appeared on my 1.5 instalation.
So I decided to update manually.
After 4 attempts I have finally given up.
Mainly 500 errors or other errors or a blank screen even when in Dev mode.
I have gone back to a backup made in May.
I did successfully install 1.70 on another directory on the same server.
It's a pity the export plugin does not work or I could have moved the content.
What can I do so the automatic update button appears?
I can't face another few hours of wasted time trying to do a manual update.