Is it normal for a hen to lay a shelless egg every now and then?

[number1newbie]

My laying hen layed an egg that was shelless for the first time! Is it something I'm doing wrong? I give them a good quality layer feed and i throw uncooked (plain) oatmeal along with grasshoppers in the run so that can scratch and find them. Should I provide her with oyster shells also as free choice? :/

 

[ChickenCanoe]

Shelless happen from time to time but I wouldn't call it normal. It could be a lot of things of which calcium is only one.

http://www.alltech.com/sites/default/files/alltech-egg-shell-quality-poster.pdf