The reason you cannot currently move the client's Retirement event to Year One or delete it, is because of the existing 'Pre-Retirement' stage to which the Retirement event is connected, or 'linked', i.e. the 'Retirement' event is acting as a 'boundary' between the one (Pre-Retirement) 'stage' and the other (Retirement).
In a situation where an individual is either already retired, or is retiring in Year One of the plan, this effectively negates (from the software's perspective) the existing 'pre-retirement' stage. In order to drag the individual's Retirement event to Year One or delete it, therefore, one will *first* need to remove/overwrite the 'pre-retirement' stage.
Now, note that one cannot delete a stage outright, but you can overwrite an existing stage with an adjacent stage. There is a quick video (made for another user) linked-to, below, which shows exactly how to overwrite the 'Pre-Retirement' stage:
This involves clicking on the Retirement stage, moving the green dot which is linked to the Retirement event to the Start event by clicking on it and dragging and dropping, then clicking OK.
Click Yes to the warning message which appears.
Once you have overwritten the pre-retirement stage, you will have freed the Retirement event(s) from being used as stage boundaries. The perforated boxes, which indicate stage boundaries, will no longer display around the event icons. You will then be free to move one, or other of the Retirement events to Year One of the plan, or even to delete the event(s), if they are no longer needed.
Last updated 02 December 2015, Release 4.0.29