Are you using S-Function block in your model? This error may be observed when creating an S-Function block with variable input port sizes. If this is the case, please see if the following helps:
1) All input ports must have a maximum size limit. For example you may have a variable sized matrix as an input to S-Function block but maximum size should be specified in the Model Explorer.
2) The variable option can be checked in the 'Model Explorer' but within a code there should not be a situation which will cause the array to increase beyond the maximum size.
3) No input port inherits its dimension from other input ports. The sizes are specified clearly in the Model Explorer.
Please check your model with respect to the points mentioned above.