TypeError message

Hey people,

On the site I am working on I have successfully created some buttons that take the play head to a to different frames. However, I have created a new button to take the playhead back to the main section which isn’t working and I’m recieveing this message. Anybody have any idea whats going wrong or what this message is saying?

TypeError: Error #1009: Cannot access a property or method of a null object reference.
at galleryNoTop_Scene1_fla::gallery_1/frame10()
at flash.display::MovieClip/gotoAndPlay()
at galleryNoTop_Scene1_fla::gallery_1/onIntroClick()

Thanks in advance,