Hello,
The front-end URL for the image is:
http://localhost/huisartspraktijkjacobs.nl/src/index.php/includes/js/ThemeOffice/tooltip.png
In the back-end, i.e. on the page where I can configure the tooltip, the URL is:
/huisartspraktijkjacobs.nl/src/includes/js/ThemeOffice/tooltip.png
The latter is shown correctly in the browser (IE7).
From looking at the URLs I decided to have a look at my settings in the 'SEO Settings' section of the Global Configuration.
It turns out that I have two options which both solve the problem:
1 switch 'Search engine friendly URLs' off
2 switch 'Search engine friendly URLs' and 'Use Apache mod_rewrite' both on
Thanks for putting me on the right track!
Sweder