Both getting one of the two errors described above.
I have also another two points to make:
1. I have another E7250 laptop on which I tested the above solutions and got identical results
2. I have successfully booted other images with different operating systems.
There is another possibility… Dell system detect has to be ON to download the W7 image, maybe the image is specifically tailored to boot only on the exact same machine? And if so… This makes no sense on many different levels. How should I go around it if the system is bricked?