Onyour DataBase You Define date values as date like,
Manufacture nvarchar(max),
ExpiryDate date,
In Your C# You Passing, Text Values of Dates like
cmd1.Parameters.AddWithValue("@ExpiryDate",txtExpiryDate.Text);
So only, The Error converting varchar to datetime
Understand how to pass the date value in c#,
Gothrough,Culture Info
DateTime now1 = DateTime.Today;
cmd1.Parameters.AddWithValue("@Date", now1.ToShortDateString());