DBUA fails. / Cannot connect to sqlplus. / ORA-01804 & SP2-0152

Trying to upgrade my single instance TEST db on Oracle Linux from 10.2.0.4 to 11.2.0.4.

From a general perspective, I have worked through a number of pre-requisite steps, and had reached the "Upgrade" stage of things.

I considered the steps to be:

1. for oratest user, point environment variables to 11g home

2. create a db listener for 11g

3. launch dbua

I don't get far, as dbua fails with following error...

There is an error in creating the following process: /TEST/db/tech_st/10.2.0/bin/sqlplus -s /nolog.

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No matter if I try to run sqlplus from 10.2.0 or 11.2.0 home, I get the following then...