Never seen this error. It might be solved by an update of Mendix 10.12; I would recommend upgrading to 10.12.14 or 10.18.3 if possible.
Does it only occur when you try to create a package (mda) or also when you run?
Otherwise: clean deployment directory (in the App menu of Studio Pro) before? Restart Studio Pro?
Have you tried with clearing deployment directory and sync with app directory and then try to create the deployment package? IF no, then i will suggest you to give it a try and if yes then manually verify if the path is correct and try with reinstalling mendix studio pro.