This means that you should ckeck your model on not committed nested objects. Let's say you have a page with a main object and some nested child objects. When you use the regular save action on this page the main object get's saved but not the child objects. If you do not do this with an onchange action in the form or with a custom save button you get the message above.
Sollution: either use a on change commit microflow in your child objects or use a custom save action where you commit the parent object and do a retrieve and commit on all the child objects of that page.
Most times you can't do anything about this error. The suggestion that this is a modeling error is most time incorrect. See https://forum.mendix.com/questions/7355/Autocommitted%20Objects%20Mystery#11193