After installing of Ewido on w2ksp4, my sunbelt-kerio PF 4.2.3 started frequently crashing by BSOD of fwdrv.sys. It disapeared after deinstalling ewido....
I run the same setup & no problems, might try a registy editor like regsupreme before reinstalling Ewido but it may have to do with the way you have Kerio configured, I've turened off ad blocking etc.