Issue merger is throwing an error message

I have full administrator permissions, but am getting the following error message when I try to merge to issues:

Errors: {} Error Messages: [karin, you do not have the permission to comment on this issue.]

The merger worked up until today and I haven't changed any of the workflow steps. Is there anything I can do to fix this? My workaround has been cloning the "child" issue, which then successfully merges into the "parent" issue.