Did you install the war yourself, or using the installer?
I'd suggest the following:
1. Clean the database (or create a new database)
2. Create a new installation of Tomcat 6 (As far as I know it really won't work on Tomcat 8 due to changes in the servlet api, although I might be wrong)
3. Copy only the openxdata.war into webapps for now
4. Send us the necessary logs (via pastebin again). Depending on your OS, there might also be a localhost.log file that could have a useful stack trace (error). If openxdata.log contains more information than catalina.log, then send that too.
The reason is that even though it gives the same result in Tomcat 6 and Tomcat 8 - the error might be totally different.
Thanks
Dagmar