Seems like you have a version problem with your project.
Have you followed the "Safe Way to Upgrade" described here?
If so, can you check the graphical API used by Unity to render in the editor? The plugin does not work with the "OpenGL Core" API (OpenGL 4.x), so make sure it uses another one.
You should also make sure that all your effects are re-baked with the appropriate version of the editor (that matches the version of the plugin). So for the v2.7 of the plugin, you should bake your effects with the v1.9 of the editor (the latest version would be the best):
There were indeed some problems with the IOS plugin that are now fixed, and it is always a good thing to keep your plugin and your editor up to date to benefit from the latest features/optimizations.
Hope this helps,