HELP! AssetBundleBrowser "EndLayoutGroup: BeginLayoutGroup must be called first"

Help! This error came up out of nowhere and I can't seem to get around it.

When I click 'Build' to rebuild my asset bundles in AssetBundleBrowser I get "EndLayoutGroup: BeginLayoutGroup must be called first"

The only thing that changed from the last time this worked was I changed the position of a few in-scene objects. I am getting this error on both my PC laptop and my Mac Laptop which are sharing the file via the collab system.

I have tried;
* Rebooting Unity
* Deleting AssetBundleBrowser and reimporting it.
* Resterting my computer
* Rolling back to the last known good collab version.

None of these have fixed it. There is no code line to look at although it does say "UnityEngine.GUIUtilityrocessEvent(Int32, IntPtr)" which seems to be something internal I can't access.

Please help! I have a tight deadline for my app on Wednesday (which means that I need this done tomorrow if I have a chance of it clearing iTunes App review) so I don't have time for a random unfixable error like this!

 

Have you solved this problem? I have the same problem.