Same problem here, but with unity cloud only.
Locally builds perfectly, but in the cloud cannot build iOS, Android or Web.
Both unity versions are the same: 5.0.1f1.
This is happening with a brand new project and last 2d toolkit version.
2.5.1
1: [Unity] Initialize engine version: 5.0.1f1 (5a2e8fe35a68)
2: [Unity] -----CompilerOutput:-stdout--exitcode: 1--compilationhadfailure: True--outfile: Temp/Assembly-CSharp-Editor.dll
3: [Unity] Compilation failed: 4 error(s), 0 warnings
4: [Unity] Assets/TK2DROOT/tk2d/Editor/tk2dEditorSkin.cs(14,25): error CS0103: The name `tk2dExternal' does not exist in the current context
5: [Unity] Assets/TK2DROOT/tk2d/Editor/tk2dEditorSkin.cs(20,24): error CS0103: The name `tk2dExternal' does not exist in the current context
6: [Unity] Assets/TK2DROOT/tk2d/Editor/tk2dEditorSkin.cs(24,24): error CS0103: The name `tk2dExternal' does not exist in the current context
7: [Unity] Assets/TK2DROOT/tk2d/Editor/tk2dEditorSkin.cs(46,17): error CS0103: The name `tk2dExternal' does not exist in the current context
8: [Unity] Assets/TK2DROOT/tk2d/Editor/tk2dEditorSkin.cs(14,25): error CS0103: The name `tk2dExternal' does not exist in the current context
9: [Unity] Assets/TK2DROOT/tk2d/Editor/tk2dEditorSkin.cs(20,24): error CS0103: The name `tk2dExternal' does not exist in the current context
10: [Unity] Assets/TK2DROOT/tk2d/Editor/tk2dEditorSkin.cs(24,24): error CS0103: The name `tk2dExternal' does not exist in the current context
11: [Unity] Assets/TK2DROOT/tk2d/Editor/tk2dEditorSkin.cs(46,17): error CS0103: The name `tk2dExternal' does not exist in the current context
12: [Unity] -----CompilerOutput:-stdout--exitcode: 1--compilationhadfailure: True--outfile: Temp/Assembly-CSharp-Editor.dll