I get this message when trying to close a particular corporation in my main country, not a recently captured C3. I am able to close other state corporations and have most automation features disabled.
I've repeatedly tried closing it over several games years, so it doesn't seem to be a matter of waiting it out.
The corporation is consistently unprofitable year after year, and it is fully upgraded. I think it makes economic sense to close it and let the workers shift to privately held corporations.
Any thoughts on what is happening and/or workarounds?