Weird problem >>> editing some products and categor

Hi,

This is a very strange problem. If I try to edit some (not all), products and categories from admin, instead of going to the edit form, it goes to the admin login menu (Admin Login Panel), and no matter how many times I log in and enter login info, when I go back to the categories menu and try to continue editing goes back again to Admin login ...

That same thing happens with 'some' not all categories, and with some products, I had to manually edited the db to enter updated price info because I couldn't do it from Admin, no matter how many times I tried...

Thank you,