I have had this problem for the last day and a half. When I try to post a message with an attachment (a PDF file only 22 kb in size), I get this error message.
You don't have permission to access /index.php on this server.
Additionally, a 404 Not Found error was encountered while trying to use an ErrorDocument to handle the request."
It only occurs when I try to attach this PDF file (although I haven't tried to post any other attachments). There have been no problems with my other posts that do not contain attachments. All the posts that failed (five or six in all with similar messages and the same attachment) were to the "Building a Repertoire" thread. The most recent one was at 8.01 pm this evening.
I have tried clearing my cache, switching off my computer and starting it up again, but without success. I don't know whether it is relevant, but my O.S. is Windows 8.1, my web browser is Google Chrome and I am on superfast broadband. Any advice would be most welcome.