The output of the blog is in XHTML transitional and the header tells it is.
The code of the advertisement does not comply to the XHTML standards.
Solution: validate your blog at http://validator.w3.org/ and fix the errors one by one. Some of them are easy (replace <SCRIPT> by <script>).

Good luck

thanks...
i'll try to fix ;)

Another question.
I'm testing 2 skin.
with nifty corners i've difficulties to run the in_text ads....while with custom it's all ok
You can see it by switch to italian version.
Why?