Finally, I got the error again :-)
The PHP log says:
[25-Feb-2009 18:37:16] PHP Fatal error: Maximum execution time of 30 seconds exceeded in D:\Programme\Apache Software Foundation\Apache2.2\htdocs\DokuWiki\inc\parser\lexer.php on line 598
The DokuWiki page itself isn't that big. But another process was using lots of CPU at the same time.
I stepped back to the editor page and tried to save again. That time, it worked. Previously, it hadn't always been that simple to save the page.
BTW, I recently upgraded to dokuwiki-2009-02-14.
Malte