Need help with thumbnail creation - pulling an all-nighter

[Michael Satterwhite]

I'm having trouble with the functions for resizing a picture uploaded to my
server. Consider the following:

$jpeg = imagecreatefrom jpeg($filePath) ; //I know this works!

$oldX = imageSX($jpeg);
$oldY = imageSY($jpeg);
$thumbH = 100;
$thumbW = ($oldX / $oldY) * 100; //I know the dimensions are correct

$thumbnail = ImageCreateTrue Color($thumbW, $thumbH);
if(!ImageCopyRe sampled($thumbn ail, $jpeg, 0, 0, 0, 0, $thumbW, $thumbH,
$oldX, $oldY)) {
print 'Error message<br />';
return;
}
//No error is produced, so the system thinks the image copy worked.

imagejpeg($thum bnail, 'thumb.jpg');

I get an thumbnail image that is completely black. I did not get an error
from the copy, so the system thinks it works - but nothing was copied.

Can someone please give some help?