Have a look at the error message in more detail. It'll tell you: such block is outputting a signal of dimension x and is driving such block, which is expecting s signal of dimension y. This will help you to find out in which block the problem is located and fix it. From the model, you can also click on Format -> Port/Signal Displays -> Signal Dimensions to show the dimensions of the various signals in your model. When a '?' is shown, it means there's a problem with inconsistent dimensions.