Want to edit node: Showing blank page

I'v just upgraded to 4.7 from 4.6.9 on a commercial site.

Now, i'm trying to convert images to products using the ecommerce module. To do that i need to select the edit tab in that particular node i want to convert.

Certain nodes, only a couple of them without any obvious relation between them, are showing a blank page when clicking on the edit tab. Actually, when i type in the address bar, lets say:

"http://mysite.com/index.php?q=node/375/edit"

, it just shows a blank page on certain nodes.

Others work fine.

What could be the reasons why they show a blank page? Has that something to do with the database?

thanks for a little assistance.