Transforming negative correlated non linear variable to linear positive correlated variable
What's a BU? Business Unit? 

Can you tell anything about the variable and target variable? Can you include the scatter plot? 

It is still not clear if the problem is not in the domain knowledge/assumptions. 

A business example:
Profit depends on sales, which is generally assumed to have a positive correlation. But after a threshold marginal sales cost exceeds profits (very expensive to acquire new customers), we can still have a (local) negative correlation. If you only have data in the 'marginal' segment, you can draw incorrect conclusions.