@Morroloan. Thanks for the additional information. it is strange that FILEINFO_MIME_TYPE is not defined for your PHP 5.3. You should check this out, because it is enabled by default as of PHP 5.3.0.
I am not 100% sure what is going on in your situation that causes this issue for you. However, this week (hopefully) I will be releasing an updated version that may help shed some light on what is gong on. So, if you can give me a day or two, you should have some better answers.