Some slicers and software include mesh error detectors. These tools are handy, but they sometimes generate excessive alerts, with too high a sensitivity and thinking they're detecting problems that in reality will have no consequences when printed. 

Such an error message can therefore occur without any real impact. Nevertheless, if in doubt, don't hesitate to contact us, if possible with the precise STL on which you're encountering this situation, and we'll look into it in detail. 

Sometimes the software misinterprets the model data, confusing millimeters (metric system) with inches (imperial system). In this case, you just have to enlarge the concerned part by a factor of 25,4 (+2540%), that will solve the problem.