When we have seen this is the past there have been two possible reasons. 

The most likely is that you have added something to your site since your last forum update that is causing a jQuery error which is then, in turn, stopping any other calls to jQuery so that the whole thing errors.  This might be another plugin or sometimes even the WP theme itself,

The other – but far less likely – is that something is hi-jacking the Ajax call during the upgrade process and thus returning erroneous data that the forum process can not recognise and process.

The former – and possibly even the latter- can usually be discovered using the web console and checking for JavaScript errors when you try the process. (https://simple-press.com/documentation/codex/faq/how-to/how-to-use-your-web-browser-console/)

Ive had a look at the console and can’t really make anything of that but this is a very basic site and theme using just “Twenty Eleven” and everything else has been updated fine, I haven’t added any new plugins and tried the update using a different theme but that had the same result?

There has to be something going on in the console… the fact that you got the spinner means an ajax request was fired which would show up in the console…  normally, there is a little plus sign by the one liner that shows it to expand for more info…

have you looked at your server php error log right after trying to see if any other info reported?

just need a bit of info to help you out…

barring finding some info in the console or in the error log, if you wanted to pass us some admin credentials, we could take a look…  you would need to PM Mr Papa, Andy and Ike the details… please also include a link to this topic so we know what it pertains too…

Thanks guys, I’ll pm you the info shortly.

I’ve just logged in, gone straight to the forum and clicked the upgrade button and it went through in seconds!

What I can’t do however is check the forum admin as the account you provided was not a Simple Press admin account (understandably) but I do see trademarks of the update so things look and should be fine. I can access the forum through the front end and it all seems to be working OK.

I couldn’t see any errors and had no trouble, so maybe it’s a local issue? Possibly something to do with your browser / plugins / add-ons / Windows firewall or similar? Just guessing really..

Thanks Ike, I’ll take a look and test some more tomorrow.

please do let us know…

Everything seems to be working perfectly now – that was all very strange. Im a bit cautious to upgrade again due to some potential downtime. Any ideas at all what might have caused this? 

I would refer you back to post #2 for the most likely causes. The fact that Ike was able to tun the upgrade suggests that whatever was at play is either (a) Not being actioned on every ajax call – or (b) only run for specific users. Maybe one of those rings a bell…

As to upgrading to 5.6.3.1 then I would recommend it. If it fails for you as a forum admin, try it with another account that isn’t one. if it still fails then we can tell you the data change to make in the database which is very simple through a tool like phpMyAdmin probably available in your hosting console.

And the most usual way to find the suspect is to deactivate other plugins until the culprit is found which then makes it easier to diagnose. By the way – if you have any sort of chat plugin active then that really SI worth deactivating while you upgrade.