access denied

I dont know if this question belong to this forum, but the problem is serius...I dont know wy my site suddenly show acces denied on the page wp-activate.php when you activat a new blog...???!! I have tried cmode 777, 755 644 (644 as default) but i thinkt something blocking this script but were?? I have installed premium plugins + plugin commander and random anti spam from peter...Is there any idés aboyt my problem.

I have asked around all forums but no answer so far..