Laravel Issues - Token missmatch

I use Laravel 5.1 for an serious project and everything is almost done.

I have an big problem and biggest issue and I dont know what is exactly the problem...

When I open some url sometimes works fine but sometimes I get this screen:

but why? What can be a problem? I on every form have

The biggest problem is becouse sometimes work without problem and sometimes show this error screen... please help.

via Chebli Mohamed