Frank, this is fairly complicated, using a number of methods.

You created a Print document.
I changed it to a Web document.

First off, put a holding message into your current Marquee: Checking for the latest message, please be patient...
If everything is working this will never appear.
Next, add a Name/Anchor of message to the marquee Placeholder.
Somewhere on your local machine, create a text file, message.txt with a single line of: Deze avond is er geen bijeenkomst wegens het slechte weer.
Off page, create a box and Link > link to file > Browse to message.txt.
Finally, in Website > HTML Code (body) put:
Code:
<script>
async function main() {
  afile = await fetch('index_htm_files/message.txt');
  amsg = await afile.text();
  document.querySelector('#message marquee font').innerText = amsg;
}
main();
</script>
When you Preview or Publish, the code looks for message.txt.
If it finds it, it reads its contents to a JavaScript variable amsg.
It then tries to place this new message into the Marquee.

If it does not find it, it displays the holding message.

To change the message, you locate it on the server - it is in index_htm_files/message.txt.
You change it there and the page needs to be told.
I added a simple Refresh Message link for this; there are better ways.
async Fetch will not work on Export website as it does not recognise file://.

async XaraWeb-Test Banner.xar

Acorn