We have our own server, so the error.log isnt that hard to find

.. but i doublechecked it and it doesnt report any errors for vb4.. i tried Members who have visited.. and this is what it says in de admincp ... >> Members who have Visited 4.0.0.22 Display members who have visited the forum. <<
when i enable it.. the forum homepage goes blank.
We have not yet put it open for our members.. they still see vb3.8.* ..we have another homepage where we installed version 3.* inserted the database...upgraded it to version 4.. Did the nessacary actions to get it running.. use the default template.. but still white..
We are really puzzled by that one.