Problem with generating thumbnails creating user error messages on upload

I am using ngg uploader 1.7.1 and most (but not all) of the time when users upload photos there are a series of error messages generating at the top of the web page as a result – the upload itself is successful but it seems that the failure to create thumbnails in the admin gallery behind the password is creating error messages (referencing invalid image dimension, division by zero, etc. on lines 567, 1026, 297, and so on) on the public page. Need to either fix the source problem or at least change a setting (e.g. not create thumbnails in the first place) to prevent the error messages from appearing. (Not critical to have thumbnails in the gallery)

http://www.friendsofhudsonparks.org/current-programs/photo-upload/

Thank you.

http://ww.wp.xz.cn/plugins/nextgen-public-uploader/