You must use a patched version of dtc which supports the ‘-@’ argument to successfully compile overlays.
Since you didn’t mention which Ubuntu distribution I can’t say for certain but I’m guessing that you don’t have the patched dtc. Try it and see. If it doesn’t work, then you need a different dtc.
If you search these groups for ‘dtc patch’ I think you will find more information. Without knowing your specific distro I would recommend patching the dtc source code and recompiling it.
Robert Nelson’s latest Ubuntu image has the patched dtc if I recall correctly.
Are you writing to SD? When using an SD to uSD adapter on my laptop here. I’ve accidentally toggle the write projection switch while putting the adapter into the card reader slot.