[NextGen Gallery] Combination with other db-using plugin

Hi together,
i wrote my own Plugin that will create and use the wp database and ran into problems in combination with ngg.
That’s exactly the code i used:
http://codex.wordpress.org/Creating_Tables_with_Plugins
(just added the activation hook to the bottom of the code)

But NextGen Gallery will stop showing pictures added to articles as long as this Plugin is activated. As soon as i disable my own Plugin it will start working again.

When manually browsing to the picture location while having my custom plugin activated i will get this error: (poorly translated from german ;D)
The gfx ./wp-content/plugins/nggallery/nggshow.php?pid=1&width=320&height=240&mode=” cannot be displayed because it’s containing errors.

When disabling my Plugin the same URL will show the Thumbnail as it should.

Does anyone know how to get arround this?

Thanks a lot