I don't know much about windows, but I can investigate on the net. Your Lenovo ThinkPad x201 has a total of 4GB RAM, Windows 7/10 occupies up to 2.5GB right after starting up.
And now, this is the part I just guess: if you allow SH3D to use 2GB, there is a negative difference of 0.5GB which causes a collision in the memory management.