You need to have the GD PHP5 Library installed. Alternatively the image crop sizes are all bigger than the images you are trying to upload. WordPress skips over these if that is the case.
First check if you have GD installed and version. You can create a test.php file with this code below. Upload to your server and browse to the file via your browser to view the result.
<?php
// Display your GD library info
$gdInfoArray = gd_info();
$version = $gdInfoArray["GD Version"];
echo "Your GD version is:".$version;
echo "<hr />";
foreach ($gdInfoArray as $key => $value) {
echo "$key | $value<br />";
}
?>