I tested your two examples:
the first one works fine, the second throw error,
You can set another temporary directory and try it again:
<?php
$uploader=new PhpUploader();
$uploader->MultipleFilesUpload=false;
$uploader->InsertText="Upload File";
$uploader->AllowedFileExtensions="jpeg,jpg,gif,png,zip";
$uploader->TempDirectory="tempdir";
//Where'd the files go?
//$uploader->SaveDirectory="/myfolder";
$uploader->Render();
?>
Thanks for asking