When customer tries to log in using FTP, they are prompted with error 530 Login incorrect.
It may have been caused by the fact that the FTP user was not completely created on the webserver because the task to create it failed or is blocked by other failed task.
- Go into Service Director > Task Manager (Tasks for 5.5),
- Search for "**" in the taskname
- Investigate, whether it is blocked by other task. You may find #2246 helpful.