Hi Vishakha,
The error might probably be stemming from some local cache or unsave changes. You could try saving/resaving the model. If that does not work, I would suggest you to try using 'hilite_system' command to visually see the mentioned block in your model and then debug it further from there. You can read more about 'hilite_system' here: https://www.mathworks.com/help/simulink/slref/hilite_system.html