Steps to reproduce:
1. Open Blender 2.78
2. Save the default blender cube as a .blender file
3. Open any Unity project or create a new one
4. Drag the .blender file into the assets into the Project window, Assets folder

Expected result: Blender model gets converted to .fbx and is usable in Unity
Actual result: the model is not imported or converted, error message asks to use Blender 2.45-2.49 or 2.58 or higher, even though the blender file was saved in 2.78

Reproduced on: 5.5.0b9, 5.6.0a1 Windows 7
Regression found in 5.4.1f1 Windows 7
Bug first appears in 5.5

Note: not reproduced on any versions on PCs running Windows 10
Note: blender also crashes if it is open at the time of importing
Note: files exported as any other format import normally