why crash sometime

thank for you share.when i used it, sometimes it crash
![018c4a25-c0c0-4add-979f-f8cdecb0ac60](https://f.cloud.github.com/assets/943827/1235940/8e98d1b8-29b3-11e3-8449-51bcdd0488e6.png)
![d27694e1-17b0-40bd-9a28-b8564a023d3d](https://f.cloud.github.com/assets/943827/1235942/95a5f620-29b3-11e3-8f62-07bf6e14772b.png)
