Thanks for your quick response! But unfortunately your solution doesn't work at my PC. I did exactly what you said, but only one link responded correctly and the other 20 didn't!
Therefore I decided to change strategy:
1. I checked the links with the DW linkchecker: there were no broken links.
2. Validation in DW: everything correct, except several files in CSSMenuwriter\cssmw(0)\treexml.xml with the description: "The prefix "mm" has not been mapped to any URI[xml]". Is this a serious problem? And when it is, how can I fix it?
3. I try to rent temporally some server space so I can test the links before publishing.
Thanks for your attention and, I hope, answer.
Kind greetings, Jan-Theo