Thanks, just noticed the problem was in the difference between the dutch and the englisch version. I did not convert eveything...
The english version uses the following statement:
=LINEST(B2:B8,A2:A8^{3,2,1},TRUE,TRUE)
The dutch uses:
=LIJNSCH(B2:B8;A2:A8^{3;2;1};WAAR;WAAR)
I simply forgot...