There is a microflow in your model that does not contain a start event. Due to a problem in the Modeler, the error that you get does not have a location, so you cannot jump to the microflow that causes the error. We recently discovered this problem and it will be fixed in version 3.0.0.
For now, all you can do is look through all your microflows by hand. We apologize for the inconvenience.
That one is fixed in mendix 3.0. But for now, you have to figure out which microflow it is manually I think... (just throw half your project away until you found the error ;-)).