Installation failure does not seem like the culprit in my case - launching R2018b from a RedHat6 Unix machine.
I get the exact same warning/error messages as OP when I try to launch this version of Matlab (from a terminal) from my main Matlab working directory. If I switch to any other directory and try to launch, then there is no issue. The other weird thing is that it is throwing warnings about various toolboxes/toolbox directories not existing - again only when launching from my "working directory" - which seem to be toolbox names that are only found inside the "toolbox_cache" for the OLD Matlab version (in my case R2011a), e.g.,
Again, once I launched Matlab R2018b from another directory things were fine. I wonder if there is something in my working directory that is pointing the newer Matlab to the wrong system/desktop/user settings??