The Confirm Open Model dialogue will appear if you issue the Open command from the Model menu after you have made some changes to the model since you last saved it. If you do not wish to keep these changes, click on OK to continue opening a clean-component table: you changes will be lost when you load the the model
If you do not wish to lose your changes, click on Cancel to return to editing your existing model. You may then choose to save the model to a clean-component table.