[UPDATE] This is an erratic bug. If you encounter it, there are a few potential workarounds:
- just wait a few minutes before trying, and it should un-stick itself as the jobqueue catches up
- or re-mark the page for translation: Make a dummy edit (i.e. add or remove an empty line) on the source page. Mark for translation. Wait a few seconds. Now resuming translations should work.
- or play with Special:AggregateGroups,
- or ask a person with server access to run the Translate/scripts/createMessageIndex.php script.
[Original task description. Initial example has fixed itself.]
When I try to add a translation, or change an existing translation, I get the error Saving the translation failed: This namespace is reserved for content page translations. The page you are trying to edit does not seem to correspond any page marked for translation.
I've tried using "remove from translation" and re-setting it, but that didn't fix it.
There was an earlier user-error where translation-markers were manually added, but I've never seen that issue lead to this problem before.