Thank you for reporting this bug, but it is already known to us.
When applying the NEN 3650 option in version 4.2.2 of Ple4Win, two warnings are likely to be given incorrectly. One about exceeding the critical buckling strain and the other saying that the allowable stress is exceeded. In reality this is not the case.
We have solved these bugs in the meantime and we will release a patched version at short notice.