Miriam_M, does the 403 error you see look like
this 403 error or does it have other content at the bottom or a different style?
Personal messages should work now, and my email is on my website, but I am in the process of changing it and don't want to publish it again on the forum because it
might be different soon.
This error is most unusual in this context and it indicates the user agent is somehow making a network request that results in that error. Since the input element in question, Preview, is a form input with an event handler (in other words, it is not a link to anything), and the only network request the script makes is to send a little XML (for validation, it looks like) to the server, to get this error when using Preview is very strange.
I know that if the server goes down or something while you have a page loaded, the form elements usually just do nothing or lag for a long time.
My suspicion is that the error is from another server, probably the one the unusual link is pointing to, and it does seem that the issue is related to that particular link (or kind of link).