buildworld fails

[Bachilo Dmitry]

I just tried to buildworld to upgrade another server from 5.5 to 6.1, but 
while it went absolutely fine yet, on this server it told me this:

===> sbin/ipf/ipf (obj)
mkdir: /usr/obj/usr/src/sbin/ipf/ipf: File exists
*** Error code 1

Stop in /usr/src/sbin/ipf/ipf.


What do I do wrong this time?
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С уважением, Бачило Дмитрий
Руководитель отдела системной интеграции
ООО "Компания СоЛинк"