Entering the End makes no never able to log on again...

[gavjenks]

So I made a mistake and built a force field 3 blocks above the obsidian platforms in the end. There is room for a person underneath, but apparently not enough room to make Minecraft happy.

So when i enter the end portal now from the overworld, it says "internal server error" and kicks me, over and over.

I am talking with my server host about how to fix the immediate problem, but what I would like to ask you guys is: What are the requirements for a legal spawn / portal transport event into the End? Like how many available air blocks does it need, etc.? I checked this ahead of time on the wiki, but it didn't say anything about it.