It's not very clear what 'load flow' refers to, in the question. It's apparent that you're talking about Simulink Models and there are bus elements in the model, a total of 50.
Though, you've inserted all the parameters in the model, the error "Undefined function or variable -YBus-" indicates that upon Simulation the Model is unable to locate the "YBus" name and hence the error.
You can define a variable with name "YBus" at the Matlab command prompt, so that it comes into context of the currently loaded model, and then try running the model again.Successful execution of the Model indicates that "YBus" was expected to be a variable and not a function, the cause of error has been resolved. If it fails, probably "YBus" should've been a function, you should investigate more in that case.
Once the investigation is complete and you know the cause of the error, you may go ahead with ensuring that YBus, is properly known to the Model before expecting it's successful execution.
Setting Block Parameters - A good link to read about how you can configure parameter values of a Simulink model, properly.
