You can validate a mapping while you are working on it through the Designer. Also, when you click Repository > Save, the Designer validates all mappings since the last time you saved. When you validate or save a mapping the results of the validation appear in the Output window. The Repository Manager also displays whether a mapping is valid.
To validate a mapping, check out and open the mapping, and click Mappings > Validate.
If the Output window is not open, click View > Output Window. Review any errors to determine how to fix the mapping.