Plugin breaking

Hello, I find a lot of plugins are causing your plugin to break… the sideoffer falls to the bottom left of the page and the plugins background image disappears completely… this happens virtually every time I install a new plugin since installing yours… from time to time I find I can install a new plugin without breaking yours but that’s rare… So is there perhaps a piece of old code in there somewhere… or a section of code that has not been written 100% correctly? Thank you for your help.

http://wordpress.org/plugins/sideoffer/