Hi,
This usually means that you have some kind of security mechanism on your server/website which blocks the saving because it sees the PHP code being sent to the server by the browser and blocks it, just in case.
In that case, you won't be able to use the view override mechanism in HikaShop.
Either you create the view overrides via Joomla
www.joomlashack.com/blog/joomla/overrides/
or manually
docs.joomla.org/Understanding_Output_Overrides
Or you turn off the security mechanism while you do the view override, or you whitelist the view edition pages of HikaShop if such a capability is available.