How can I remove "new_from_date" attribute content in product grid using "Mass action" feature ?
Thank you for your help.
Do you have that column on Catalog -> Products grid?
I've tested on a pretty clean Magento (is a vanilla installation with some custom modules but no important changes).
I've made a small video. You can download or see the file here: https://dl.dropboxusercontent.com/u/798040/products-mass-attribute-update.ogv
As you can see, following your steps works fine.
(I'll delete this video in the next days)