Thought I would post this, since after some considerable head scratching, was able to solve this error. We have been using VCO for quite some time now, but troubleshooting, especially without a debugger, can be a real bear.
This error started to appear on a workflow which had been working fine up recently. Nothing had changed within the workflow or the configuration elements that feed it. For some reason, VCO (4.1.1.build 733) gets randomly removed from this server. We don't know whether it's a product glitch or somehing else, as there no indication in the logs, however it necessiates a re-install to get it working. When it was last re-installed, the VIX plugin was skipped and VCO threw the above error. Somewhat misleading on the error message for sure. Anyway, just posting in case anyone else runs into this and forgets to check the VIX plugin being properly installed.
