Memory error with type L"" in Win32

Question

Here's the code for my paint method in my Win32 project:

case WM_PAINT:
    _tcscat_s(greeting, sizeof(greeting), LoadedFile);
    hdc = BeginPaint(hWnd, &ps);

    TextOut(hdc,  
        5, 5,  
        greeting, _tcslen(greeting));

    EndPaint(hWnd, &ps);
    break;

I am consistently getting the error that either the stack around greeting or around ps is corrupted. To be clear, greeting is initialized like:

TCHAR greeting[100] = _T("Welcome! Your file is ");

And LoadedFile is initialized like this:

TCHAR LoadedFile[100];
LoadedFile[0] = 0;

LoadedFile is not yet changed by anything, so it shouldn't be adding anything to greeting. I've tried things like

sizeof(greeting) + 1

Which just shifts the error. Not sure what's wrong here.

Edit: Without the _tcscat_s(), call the window loads normally

Answer 1

Well, I found the problem, even though I don't really understand why the solution works. I just changed

 _tcscat_s(greeting, sizeof(greeting), LoadedFile);

to

_tcscat_s(greeting, 100, LoadedFile);