[O] DTD prohibited

[AW]

Hi,

I'm drafting documents with orgmode. Once in a while I have to export them to 
html and send them as an attachment to an email, telling the recipient to open 
the file with word.

Now, Word no longer can open the html-documents produced by orgmode. The error 
message is (translated from German): "DTD prohibited".

I tried on two PC, both times Word 2010, same result: error.

Example of orgmode-file to be exported:


* Export
Bla bla bla


Exporting to odt and opening with libre writer: no problem.

If anybody got the same error and knows a solution, I' be thankfull,

regards,

Alexander