Hi Timber,

Goto Dashboard -> Users. Click on the link Administrators. In Blogging permissions change "XHTML validation: Force valid XHTML + strong security" to "Basic security checking" and do the same with 'XHTML validation on XML-RPC calls:'
In fact I think you can get away with changing only the latter but you should test that yourself.

Good luck

Thank you Afwas,

It didn't help as that was the settings already, but I found the solution at the same location.

I've turned off the Security Filters for CSS and Object.

That did the trick.

Thank you for guiding me to the right spot.

Michael