"it Was Not Possible To Determine The Dimensions Of The Image.", phpbb3 images and avatars

[Marklo]

I looked all over this forum and the phpbb forums for an answer, but found nothing I could understand or was relevant to my situation.

My problem is that members of my forum cannot upload or get offsite pictures to their profile avatars and they cannot get pictures using the [img] in their signatures. yet posting a picture using the [img] works just fine.
I get "It was not possible to determine the dimensions of the image." when uploading the image from the computer, it lets me open up the file I want to upload it from, but when i hit "ok" it does not fill in the file location, so it never uploads it.
I set the file I want the avatars uploaded to to 777 using ftp, and still nothing. The PHPbb admin permissions for avatars and signature [img] bbcode are set to allow. So I am not sure what, or where the problem is.
The file is writeable and the permissions are allowed. Im thinking it is the host, but I am not sure?
Thanks for the help.