In the Windows PATH environment variable, MATLAB Runtime (MCR) must appear before any MATLAB installation paths. Having them the other way around could be caused by a previous installation of the Prerelease version of the Web App Server.
Make sure that MATLAB Runtime (e.g. C:\Program Files\MATLAB\MATLAB Runtime\v94\runtime\win64) appears before MATLAB (e.g. C:\Program Files\MATLAB\R2018a\bin) and try launching the Web App Server again.
1. Go to Control Panel > System > Advanced system settings > tab "Advanced" > Environment variables.
2. Under "System variables", find the variable "Path" and click Edit.
(The Variable value likely contains several paths, too long to conveniently edit in the small field. For convenience, you may find it easier to copy the value to Notepad or a similar editor, edit it there and copy it back after making the changes.)
3. Edit the path so that the path to the MATLAB Runtime is listed before the path to MATLAB.
The path of MATLAB Runtime has the following format:
C:\Program Files\MATLAB\MATLAB Runtime\<version>\runtime\win64
(Version v94 is for R2018a. For a list of versions refer to https://www.mathworks.com/products/compiler/matlab-runtime.html.)
The path of MATLAB has the following format:
These are the default installation folders. Your paths may vary depending on where you installed MATLAB and the Runtime.
For example, initially the Path variable value might look like this (MATLAB before MCR):
It has to be corrected so that MCR is listed before MATLAB: