I understand your problem.
The problem is in the query. As you know that CostCenter, Category, Course Code can have multiple data in table. But the combination of all the three can have only one record.
So, your queries should be like,
CostCenter:
Select distinct [CostCenter] from [tblDiscipline]
CategoryBind:
Select distinct [Category] from [tblCategory] WHERE [CostCenter] = @SELECTED_COSTCENTER
CourseBind:
Select distinct [CourseCode] from tblTrainingPlan where ([Category] = @Category AND [CostCenter=@SELECTED_COSTCENTER])
BindData:
Select * from [tblTrainingPlan] where ([CourseCode] = @CourseCode AND [Category] = @Category AND [CostCenter=@SELECTED_COSTCENTER])
Mark it as answer if it is helpful