Codeigniter do_upload()在“成功”中悄无声息地失败了

I'm using CodeIgniter to write an image upload form. I've previously got similar code to work for a different site. At the moment - the code for receiving a multipart/form-data image is failing silently. While configuring the server/script I received errors, such as incorrect filepath, dissalowed mime-types, but now I get nothing.I'm using CodeIgniter to write an image upload