I am not sure why this is happening unless the Oracle listener is not running. If the listener is up and you are still seeing this error, you might want to consider upgrading the database manually rather than via the Database Upgrade Assistant. To do this, review the procedures in the Oracle 10g Release 2 Database Upgrade Guide.
There is a section in this guide titled "Upgrade the Database Manually." This will provide you with a step-by-step procedure for manually upgrading the database, rather than using the DBUA.
Dig Deeper on Oracle database installation, upgrades and patches
Related Q&A from Maria Anderson
I have been trying to install Oracle 8.1.7 on SUSE Linux 9.0 and got the error: "Error in invoking target install of makefile /opt/oracle/...../*.mk." Continue Reading
Can I use /var/opt/oracle/oratab to specify listener information? Continue Reading
How many database instances can be created on an Oracle server with an installation drive containing 15 GB free space? Continue Reading