Some people identify it straight out as writers block, some people just think they're 'not ready' or 'the character and story haven't developed yet.' Call it what you want, I'm going to call it writers block.
If you're writing a screenplay about an aging boxer who is struggling to find the energy and motivation for that last fight, or if you're writing about a teenager who's not ready to take on his duty to save the world from terrorists --- whatever it might be, it is interesting to see how your inner conflict is something that your character is going through as well.
Your inner creative block is a natural thing for all humans. There are elements of it that are similar for your character. In fact, when you think about it - that's what films are about... characters who reach their limits, struggle with them, and then surpass them to save the world/get the girl/win the fight. So use your problem as part of the solution. What does your block tell you about your character?
Interestingly, a block often comes at the point when you have written a block for your character. For example, you may write twenty pages of a script with ease - and it's the best thing you've ever written. And then you make the girl dump your character, you blow up his house, and you make him lose his job. And then you're stumped, you've lost your flow.
What happens is that you identify with your character more than you realize, you begin to find yourself lost, like your character. But rather than think 'meh, I'm out of ideas.' You're not, your character is out of ideas. And if you really delve into that, then you are going to find really exciting ways to move on with your script.
It's really helpful to communicate with your writers block. You may feel a bit schizophrenic doing it, but it works. When you feel that voice in your head saying 'the idea isn't there yet' - you need to hold it accountable, you need to find out why. So, give your writers block a name. For this exercise, I'm calling mine Harry.
That's it. It helps.