# Rotation and Matrices Help

**URL:** <https://forum.kirupa.com/t/rotation-and-matrices-help/300567>\
**Category:** flash\
**Created:** [November 23, 2009, 7:14pm UTC](https://forum.kirupa.com/t/rotation-and-matrices-help/300567 "2009-11-23T19:14:50Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![Nejuf](https://avatars.discourse-cdn.com/v4/letter/n/ecc23a/32.png) [@Nejuf](https://forum.kirupa.com/u/Nejuf)\
**Post date:** [November 23, 2009, 7:14pm UTC](https://forum.kirupa.com/t/rotation-and-matrices-help/300567/1 "2009-11-23T19:14:50Z")

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Hello,

I am using Corey Oneil’s collision detection kit, but I am having a problem with rotation.

In my code I have:

myItem.rotationY = 180;

However, during a collision detection, having it rotated like this causes an error with this line:

transMatrix1.concat(currentObj.parent.transform.matrix);

The error is simply “Error #1009: Cannot access a property or method of a null object reference.”

I have not really worked with matrices and rotation so if someone could help me that would be great. Do I need to make a matrix rather than just doing the rotationY or should I change something else? I cannot manually change the movie clip because it throws off the animation and armatures.

Thanks.