OC 6.1 linker error

hi,

would you help me to solve the linker error connected to the StepBasic_LengthMeasureWithUnit class. it has worked well with the version 5.2, oc 6.1 makes problems.
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the code were the class is used:
DeclareAndCast (StepData_StepModel, po_model, o_step_reader.Model());

double d_vc;

for (int i = 1; i NbEntities(); i++)
{
if (po_model->Entity(i)->IsKind (STANDARD_TYPE(StepBasic_LengthMeasureWithUnit)))
{
DeclareAndCast (StepBasic_LengthMeasureWithUnit, po_lmwu, po_model->Entity(i));

d_vc = po_lmwu->ValueComponent ();

if (m_eq (d_vc, 25.4, 1e-8))
{
d_Unit_Value = 25.4;
break;
}
}
}

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one of the linker errors:
unresolved external symbol "public: double __thiscall StepBasic_MeasureWithUnit::ValueComponent(void)const " (?ValueComponent@StepBasic_MeasureWithUnit@@QBENXZ) referenced in ...
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best regards,
adrian