Hi,
Could you provide more details about the error? More details (eg. error stack trace) should be available in vRO log files at /var/log/vco/app-server/ (the main log file is server.log).
The editing of the content coming from a plug-in is usually disabled intentionally. If you want to experiment with some workflow, you can duplicate it (there is a command for doing so in the vRO Java client UI) and edit the duplicated copy.