Steps to repro:

1. Open attached project and 'ProgressiveLightmappingExample' scene;
2. Open Lighting Settings window (Window>Lighting>Settings);
3. Disable 'Baked Global Illumination' checkbox;
4. Click 'Generate Lighting' button.

Actual result:
Editor starts to generate lighting for the scene after pressing 'Generate Lighting' button.

Expected result:
'Moving file failed' popup window is shown.

After closing it following errors are shown in the Console:
- 'Failed copying the texture from 'Temp/GI/9aedcfd5bff83ff289b3bca52939149e/Lightmap--1_comp_light.exr' to 'Assets/Scenes/ProgressiveLightmappingExample/Lightmap--1_comp_light.exr'.
-' Failed to reserve memory for scene-based lightmaps'
- 'Integrate failed on Write Lighting Data job.'
See attached video.

Regression introduced in Unity 2018.1.0.

Notes:
- Reproducible in 2018.2.0a1, 2018.1.0b2, 2018.1.a4;
- Not reproducible in 2017.3.0p2, 2017.2.1p2, 2017.1.3f1;
- Could not retest in 2018.1.0a1-a3 since Unity crashes on opening the project or nothing is being rendered;
- Reproducible on Windows and Mac;
- Reproducible only when both Realtime GI and Baked GI are disabled;
- Reproducible only when PLM was set as the lighting backend; not reproducible when Enlighten was set;
- Baking GI for the second time doesn't expose the issue anymore.