uploading problem

i tried to upload a batch of models
it was a folder with 4 sub folders in it for different 4 models
each sub folder has 6 png preview images and 3 RARs

but when uploaded i found that all preview images are uploaded 4 times
and also when uploading a one separate model (not using batch uploader ), sometimes the uploading proccess stops and sticks there for no reason and i had to re upload it again from beginning

how can i avoid those problems please ?

thanks in advance