The error is shown by the following scenario.Login in as Admin User to the AWI and create a simple, restricted user. Assign no User Group and only give the privileges shown in the screenshot below:
<Please see attached file for image>

<Please see attached file for image>

Next, create a workflow with one job for this user. That means, the name of this workflow must start with WRZKLB
<Please see attached file for image>

Start the workflow with
Execute once -
Wait for manual release:
Log in as the newly created, restricted user to AWI and open the
Process Monitoring. There you see the job in
Waiting for manual release:
<Please see attached file for image>

Open the Monitor. There,
Modify can be clicked, i.e. it is editable:
<Please see attached file for image>

Right click on the job and select
Open Monitor:
<Please see attached file for image>

The
JCL is opened. The
Modify button is greyed out (deactivated) and the
JCL is write protected and not editable:
<Please see attached file for image>

For comparison, open the Java UI (12.0.5) with the restricted user and do the same procedure. I.e. select
Monitor -
Open generated Job. Here the JCL is not write protected and can be edited and saved:
<Please see attached file for image>

I.e, using the same user rights (see first screenshot above), the behavior is different in AWI and Java UI.
In Java UI (V12 and older), editing the generated JCL was and is possible with these rights (see first screenshot above). In V12 AWI it is not possible anymore.