Sites broken when turning Ads on

Hi,
I just downloaded Pro sites to use it as an ad manager, however, as soon as i turn the ad module on, i am not able to load any of my sub-sites anymore. I get this error:
Error 324 (net::ERR_EMPTY_RESPONSE): The server closed the connection without sending any data.
These sites are using the twenty eleven theme.
They are working fine as soon as i turn ads off.
It gets broken whatever code i enter as an ad, and also if i don't put any.
I'm running the very last version of Wordpress (updated today) with the last version of buddypress.
I can still access the dashboards.
Thanks