Dear Friend,
This error mainly occurs when you are trying to insert a nvarchar value into a data field of type int.
Check with your sql table that which fields are of type int and at the same time check from your code that you are entering correct entry into the field types.
This is a generalized error. Please follow the link for more explanation:-
162,000 results on conversion failed when converting the nvarchar value to data type int
Please don't forget to mark this as your answer if it helps you out.
Thanks