[Plugin: WP User Frontend] Cannot upload media in frontend

Hi everyone,
Im using the latest WPUF and WP versions. All working well, but for some reason i cannot upload/add media through the front-end posting sytem. I have selected the ‘rich text full’ option in the WPUF plugin settings. The ‘add media’ icon does show up. But once i click that button and start uploading an image i get the error ‘Error uploading. Please try again later’ (translated, so the exact English message might differ). The
permissions of the folders should all be fine..

Is there anyway to fix this?
Thanks, Robbert