If you have manually upgraded to 8.0 from a previous version of Pentaho that used a DI Server and are not able to login or run transformations perform one or both of the following steps:
Check the file size of the pentaho-solutions/system/pentaho.xml file.
If the file size is 0 KB, then the file is corrupted and must be replaced.
To resolve this issue, copy the file from your 7.1 DI server to the 8.0 Pentaho Server.
