I don’t see an http 403 error such as this as being connected to WP or SP themes or even cookies. This is the server declining the URL being requested due to some sort of security setting. And the hosting support really should be able to put their finger on the problem.

But – and I am far from an expert on this sort of thing so this is partly guesswork on my side – I would assume that the support will need to know the URL that was being requested. So for that you would need to know the slug of the new topic the user was creating. And a good question would be – did the topic actually save?

I could see this happening – for example – if the topic slug just happened to be identical to a folder name which would be protected from being opened. Unlikely, because the full URL of a topic includes the forum slug, but I just use this as an example. I just think it is important to know for your hosting support to come to a conclusion.

I also believe I am correct in thinking that the particular display your user saw is Internet Explorer specific. You might want to check with them which version of IE this is because I also believe I am right in thinking that WP has dropped support for older versions – possibly anything below version 8 or even 9. So knowing this information might also prove useful.

Dear Andy, 

thanks for your response. 
I mentioned the possible issue with the browser to that person who reported the problem and it was indeed a problem with the Internet Explorer that caused the problem. I will actually ask which version she used. 
She said she tried Chrome and was now able to post without issues. 

Thanks for the hint!

Warm regards,
Sebastian

Excellent. IE always was a problem. I think WP still supports 9 and 10 however.

hopefully no on is still using IE 9 and 10…  both are very old…   There is IE 11 for those still not on Windows 10… and then Edge which is the best browser MS has done (for Windows 10)…

I found out that the user who experienced the issue was using Internet Explorer 11. 
However, I checked with me own IE 11 and had no issues posting. 
Not sure why there was an issue but sometimes we just can’t figure out anything if an error is not reproducible. 

I also truly hope that there are only very few people left using IE 9 and 10. As a web developer who has gone through optimizations for IE7, back in the days when we still had to, I am more than happy to just drop any optimization for outdated versions of the IE. It is just too painful and fortunately the numbers show (Google Analytics confirms) that IE 9 and 10 are just not anymore relevant for our website. 

Let’s hope it is a one-off…

Coincidentally – WordPress announced over the weekend they are dropping support for IE 8, 9 and 10 from their next major release (4.8). I thought they had already but there you go.

WP IE Browser Support

Yes!

And wow … that’s good news!
Since WordPress is such a big player, this will have an impact on how people deal with browser versions and how much communication around the necessity to upgrade or shift is happening. 
I am very happy to hear this. 

As, indeed, are we.

It may cause a few problems of course. I know of a few forums populated largely by older, less techie-aware users, some of whom we know are still using older IE versions. Often they are frightened to update. But they are clearly a declining number at long last.