Error "Cannot insert explicit value for identity column in table" using C#

I'm having an issue with a simple local SQL database. I'm not very knowledgeable with databases or accessing them using C#, so any help would be appreciated. I'm trying to add an entry to one of the tables in my database using C# through Linq to SQL. Here is my a snippet of the code.

using (DataClasses1DataContext db = new DataClasses1DataContext())
{
    tbl_Inventory inv = new tbl_Inventory();
    inv.Title = addTitleTextBox.Text;
    inv.Model = addModelTextBox.Text;
    inv.Category = addCategoryTextBox.Text;
    inv.Quantity = int.Parse(addQuantityTextBox.Text);
    inv.Price = decimal.Parse(addPriceTextBox.Text);
    inv.Description = addDescriptionTextBox.Text;

    db.tbl_Inventories.InsertOnSubmit(inv);
    db.SubmitChanges();

    int id = inv.IdProducts;

    MessageBox.Show($"Item creation successful. Item number is {id}");
}

I keep getting the following error:

Cannot insert explicit value for identity column in table 'tbl_Inventory' when IDENTITY_INSERT is set to OFF

My table has a column called IDProducts which is used as the identity column to increment by 1. I can add entries within the Visual Studio design window and it adds the entry with no errors with the increments working correctly, but not when I run my code. The thing is my code is not trying to assign a value to IDProducts. I tried deleting IDProducts and adding it back, but I still get the same error. I have one other table I created through Visual Studio the exact same way with very similar code to that above which adds entries to the table and I have no issues. I'm not sure what I might have done differently.