I am seeing a really strange phenomenon on a single page (http://can.org.united kingdom/training/training-diary) on our wordpress site. The page showing the strange behavior is processed by single.php and also the publish includes a shortcode inside it. The shortcode is:

[tcal tag=course]

This shortcode should produce a table that contains all of the posts labeled with 'course' inside the current category. Now we all know the code works because it was working today and, basically put an echo at the end from the shortcode function then I can tell the relevant table hase been built and it is begin came back through the function.

Issue is, the page simply shows as blank ... nothing whatsoever turns up.

Also, even stranger still, after just checking again, the entire site shows as blank ... e.g. basically visit the webpage http://can.org.uk i quickly see nothing whatsoever - a minimum of on my small home laptop it shows blank, on my small work pc it appears to operate all right (aside from the page pointed out earlier).

I'm able to log in to the dashboard and all sorts of looks all right. I haven't any plug ins installed.

Anybody know what is failing here?

Might it's "headers already sent"? Try activating WP DEBUG on config file and hang error confirming to any or all, I am confident it will likely be header problem.

Check, if on plain .php file you do not have space between ...?> <?php... somewhere.

It is best to just return the creation of your shortcode , not echo it. should you just output it , Wordpress will require proper care of the rendering for you personally.

this is a simple one , for example :

function test_function($attributes){
    return "<p><b>SHORTCODE TEST:</b>
  <br/>these are the attributes ".
    implode($attributes," ")."</p>";