I can reproduce this now. Holger’s post below agrees with what I see.
I cannot reproduce this. I find that when I add the basis set named mybasis, the computation succeeds with no problems. When I add the basis set named mybasis-decon, the computation fails as Psi can’t find the basis set.
How did you add the basis set? I suspect that I need to add it exactly the same way that you did to try and reproduce this error.
What version of Psi4 are you using?
Lastly, please use triple backticks instead of > to indent input and output files in the future.