Saving a locally created Bitmap

Seems like this ought to be an easy one. Essentially, using managed
C++, I'd like to be able to create a Bitmap locally, set the pixels to
particular colors, and save the result. Everything seems to work fine
except that upon calling the Bitmap's Save function I always get a
status of "FileNotFound" and it creates a file with 0 size.

The Code:

void CChildView::Test()
{
Gdiplus::Status stat;

Bitmap bmp(2048,2048,PixelFormat24bppRGB);

Color red,grn;
red.SetFromCOLORREF(RGB(255,0,0));
grn.SetFromCOLORREF(RGB(0,255,0));
int i,j;
for(i=0;i<2048;++i)
{
for(j=0;j<2048;++j)
{


if(i==j)
stat=bmp.SetPixel(i,j,grn);
else
stat=bmp.SetPixel(i,j,red);
}
}

CString sPath("c:\\test.png");
WCHAR wszPath[256];
MultiByteToWideChar( CP_ACP, 0, sPath,
sPath.GetLength()+1, wszPath,
sizeof(wszPath)/sizeof(wszPath[0]) );

stat=bmp.Save(wszPath,&ImageFormatPNG);
}

I should mention that yes, Gdiplus is initialized prior to entering
this function. Status (stat) remains "OK" until the Save operation,
where it changes to "FileNotFound". What am I missing here? I've had
the same problem with different file types (BMP rather than PNG, for
instance).