Upgraded to Pro and am now getting a TypeLoadException

Just turned on my free 30-day trial of Unity Pro. My current project now suddenly stopped compiling and I get the following error:

TypeLoadException: Could not load type 'UnityEngine.MeshSubsetCombineUtility+MeshInstance[]' from assembly 'UnityEngine, Version=0.0.0.0, Culture=neutral, PublicKeyToken=null'.

UnityEngine.InternalStaticBatchingUtility.Combine (UnityEngine.GameObject[] gos, UnityEngine.GameObject staticBatchRoot, Boolean generateTriangleStrips) UnityEngine.InternalStaticBatchingUtility.Combine (UnityEngine.GameObject staticBatchRoot, Boolean combineOnlyStatic, Boolean generateTriangleStrips) UnityEditor.PostprocessScene+UnityBuildPostprocessor.OnPostprocessScene () I didn't change anything. Just upgraded and clicked the Play button. Any suggestions?