I also had a problem on upgrade on Windows Server 2012 R2.
Xeams log reports:
2018-12-04 11:32:31,740 ERROR [/].[jsp] - Servlet.service() for servlet jsp threw exception
org.apache.jasper.JasperException: Unable to compile class for JSP:
An error occurred at line: 27 in the jsp file: /NewPageHeader.jsp
JspValidator cannot be resolved to a type
24: %><!DOCTYPE html>
Homepage was blank.
I downloaded Installer, backed up config directory, installed and copied "config" directory over the new (not recommended, I thought it would recognize an existing installation).
I had to kill two javaw.exe ?zombie processes before I could install.
Now is working.
