Javatest 4.2 (applicable to earlier versions as well).

Start the Harness in batch mode as following:
> java -jar javatest.jar -ts -preferred <ts> -config c:/myconfig.jti -keywords interactive -runtests
It will work OK (assuming you give existing testsuite and ocnfiguration). Now try to run:
> java -jar javatest.jar -ts -preferred <ts> -keywords nteractive -config <c:/myconfig.jti> -runtests

Harness will say: cannot set the configuration from file "c:\myconfig.jti"; it has already been set from the file "c:\myconfig.jti".
The message is quite confusing...

Harness is probably right saying that because according to javatestCLI.pdf/ "Setup Commands" / "Specifying KeywordsWith keywords":
----
When creating a command string that specifies keywords, include the commands
in the following sequence:
1. Include the commands required to set up a configuration.
See Set-up Commands for a description of the commands.
2. Include the commands to specify keywords used (keywords expression).
3. (Optional) Include a task command (such as runtests).
See Task Commands for the commands that you can include.
----

But that error message (and other similar messages from CLI processor) should be really corrected to be more user-friendly. It should try to explain what user did wrong and give some suggestion how to fix that.