File uploaded is missing

Hello everyone!
In my Events booking form I have 2 upload fields for the user picture. It seems that it all work but when i go to the backend the picture field is empy. It shows as no file was upload.
Any idea what could happen?
Thanks

I realized that sometimes it does appear in the backend like this
Current File 1457376845705.jpg Download
But the download link is like this
myweb.org.tw/administrator/index.php?opt...me=1457376845705.jpg
so when I click on it Joomla request to log in in the backend again.

I tried to delete the /administrator/ then it works, ( myweb.org.tw/index.php?option=com_eventb...me=1457376845705.jpg )
i can download the picture.. Is it something that i am doing wrong in the setup? or other people have the same problem?

Thanks

Sorry...
Now I know when the picture is there or not.
In the registrants tab of Events Booking, if the member is in a group (group registration) then the picture or file is missing.
When the user was registered as individual registration, the picture is there but with the wrong link (added an extra "/administrator/" )