Well, I fixed numero. I have never seen anything like this before. The URL for the foursquare link ended with a
? and it should not. I removed it and now it can be edited normally. For some reason, the only thing I can think of, is that this must have somehow been tripping up the security the web host has applied at the server level.
I only figured this out by making a copy of numero and slowly removing data until info until it would save without the 403. I only decided to do this after making sure I could add and edit other entries without the error. So I determined it must have been something specific to that entry.
I guess you just started getting this error because the webhost made changes at the server level and has been tweaking them. All speculation of course but its the only thing I can think of that makes sense.
Hope this helps!