Silverstripe is often Buggy :
Look @ this Line 142 till 155 in File Image.php :
$file = ASSETS_PATH . "/$class/$file";
while(file_exists(BASE_PATH . "/$file")) {
$i = $i ? ($i+1) : 2;
$oldFile = $file;
$file = ereg_replace('[0-9]*(\.[^.]+$)',$i . '\\1', $file);
if($oldFile == $file && $i > 2) user_error("Couldn't fix $file with $i", E_USER_ERROR);
}
if(file_exists($tmpFile['tmp_name']) && copy($tmpFile['tmp_name'], BASE_PATH . "/$file")) {
....
WTF is BASE_PATH used?