The feature dataset contains a grid feature class, but the tool is unable to validate it because the feature class suffix does not match the dataset name. This could happen if the feature dataset was renamed after the grid features were created in it.
Check the name of the feature dataset and the grid feature classes. Make sure the suffix of the grid feature classes within the dataset match the dataset name. If there is a mismatch, rename the feature dataset to match the suffix of the grid feature classes, or use a feature dataset that has not been renamed after grid features were created in it.