The enable/disable box is under the macro icon. E.g. (see the checked box below),
If you work in the Keyboard Maestro Editor, it does link the name with UUID. But since you are changing the name elsewhere, KM does not know whether you are intending to trigger the old macro whose name was changed to the current one, or that you want to trigger a new with this name. Whereas, the UUID is unique, and it does not change even you have changed the macro name. Therefore, using UUID is a better choice in most cases when you use script triggers. I hope this makes sense.
This error tells everything. It means there is no active macro with the given name macro.
Either the macro is disabled in someway (macros must be enabled, and in macro groups that are enabled and currently active), or a macro with that name does not exist at all (i.e., you may have changed the name of the target macro). Since you've been running it before and if you did not change the name, it's more likely that the macro is in the disabled state.
My guess is that KM only looks for the given macro name in the enabled macro list. If it does not find it, it gives the error report as you've seen.
@peternlewis, I'm wondering, when the given macro name is not found, is it possible for KM to continue to search in the disabled macro list, and when it finds it, it reports that the macro is disabled; if it does not find it, it reports that the macro with the given name does not exist. In this way, we have more clue about the error report.