Ok i understood the problem :
- if i use the structure uploads/.../years/month/ i have the "When you send a message an error has occurred."
- if i use the structure uploads/.../user_id/ i can upload images (as admin)
I have Pan Moderator 0.5.6.2 (Allows you to moderate the names of the authors of posts, post the date and date of registration.), i guess the bug in the date structure is because of this, like i have some admin error message about the date with that extension.
I have another problem, when i try as user, i can not post an image (each time i have the "your message has caused us to suspect. it will appear after the approval by the moderator"), it always need the admin approval.
How can i disable this suspect / approval behavior ?
Edit 2 : the problem seems again due to Pan Moderator 0.5.6.2, i uninstalled it, and now as user i can upload/post images