Player gets stuck on collision when jumping up a platform.

My character gets stuck if trying to jump up on a platform while running towards it. It has a box collider and a sphere collider.
Like this: http://i.imgur.com/ov5bHdw.png

Any suggestions on how to fix this?

This is a bit late :), but I had the same issue.

Just after the line that reads horizontal axis

float move = Input.GetAxis ("Horizontal");

added the following line

if (!grounded && Mathf.Abs(move) > 0.01f) return;

So, if the player is not grounded and he is moving then just return and do not execute any movement code.
Again, I assume your are using tutorial script.
So, the whole FixedUpdate looks like this

void FixedUpdate ()
{
	grounded = Physics2D.OverlapCircle (groundCheck.position, groundedRadius, whatIsGround);

	anim.SetBool ("Ground", grounded);

	anim.SetFloat ("VerticalSpeed", rigidbody2D.velocity.y);

	float move = Input.GetAxis ("Horizontal");

	//prevents the player from getting stuck into platform
	if (!grounded && Mathf.Abs(move) > 0.01f) return;

	anim.SetFloat ("Speed", Mathf.Abs (move));

	rigidbody2D.velocity = new Vector2 (move * maxSpeed, rigidbody2D.velocity.y);

	if (move > 0 && !isFacingRight)
		Flip ();
	else if (move < 0 && isFacingRight)
		Flip ();
}

There is new unity component called platform Effector 2D that will allow you to do that:
more info here:

If you are using the tutorial script, just add this ‘if’ before this line:

if (grounded)
    rigidbody2D.velocity = new Vector2(move * maxSpeed, rigidbody2D.velocity.y);