solid 226 is 20 node hex element - the element type 1 you have, so your mesh, might be different to that -perhaps you have tet4 or hex8 or wedges also, and not hex20 element.
You would need to have a mesh of only higher order brick elements (20 node hex.) in order to use/switch to the soild226 - if you do not have these elements then you cannot switch
You are navigating away from the AIS Discovery experience