Erik Kostson
Ansys Employee

Try to run it first without the membranes (so no snippet and
normal shells with bend. + membr. stiffness) and see if it runs. If it does not
then, you need to make sure that you have restrains, so for a sphere we could
use an eight of the model with symmetry and that should be well restrained to
take the pressure.

In general though, and if it does not run with the standard shell
(so no membrane formulation), then the below will help you:
First the snippet is (do not need the other 2)
Typically, membranes do not have an out of plane stiffness so we
need that before we apply load to it.

So we need one step where we apply the inistate command (search
the apdl manual for inistate) for prestress on the membrane and then a second
step where we actually apply the pressure load.

Search for inistate and membrane and there will be lots of info on
this forum and on the web, e.g., :

All the best