Process followed shown below and supporting images attached. 1. Created a new project folder: Test1 2. Added a single .asc Lidar tile to folder: Test1 3. Opened QGIS 2.18.16 4. Created new project and saved the empty project as test1.qgs 5. Closed QGIS when it closes without any error. 6. Open QGIS and test1.qgs project. 7. Do: Raster > Miscellaneous > Build Vitual Raster (Catalog)... (see image Step 7) 8. Completed the Build Virtual Raster dialogue input box selecting the .asc file and naming the output file DEM where the DEM file is saved in folder Test1 (see image Step 7 and 8) 9. See image Step 9 showing DEM created 10 Save project and exited QGIS causing crash (see image Step 10) 11 Also supplied image of Test 1 folder contents