Question on calling a method from different project and namespace

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C#

Hello all,
am using Visual Basic .NET and C# in the same solution but different project and namespace. am trying to call a method from different project in VS 2015 and was working perfectly because I just added project reference. now I upgraded VS 2015 to VS 2019, here the old methods still working perfectly but I got problem when I created new methods in the same class as before, mean it doesn't recognize my new method like others which created by VS 2015. Here below i just added for giving u my code style .

public ArrayList categoryList()
{
dInvent = new DInventory();
    return dInvent.GetData("GetCategoryName", true, "Category_Name");
}

public ArrayList ITList()
{
    dInvent = new DInventory();

    return dInvent.GetData("GetItemType", true, "Item_Type");
}

The First method (categoryList()) was created in VS 2015 and still working perfectly but I can not able to call the Second method (ITList()) , but i used the same procedure for calling both in VB.Net.

What I have tried:

I have tried to check all again even just trying to add a reference again but still i can't able to call a new method.