Steps to reproduce:

1. Open attached project
2. Select 'orange.jpeg' file in the Project window
3. Change it's texture type to 'Sprite'
4. Notice the following error being spammed to the console eahc time you slect/deselect the image:
Assertion failed on expression: 'translated != kInvalidEnum'

Notes:
The error seems more common when the Inspector is visible.
Not all texture types show the error, for example 'Default' & 'Normal Map' doesn't seem to cause the error. Haven't tested all the types.

Does not reproduce with: 5.6.0b8