can't edit

Martin, there is a time window for editing posts which is 2 hours (as stated in the forum rules) this is to make sure that the continuity of a thread is kept making the sequence of events legible, unfortunately some posters were removing their posts after getting an answer so preventing others from getting the help they need as they could only see half the story.

2 hours seemed reasonable enough time to make a change to a mistake or add some info.

I would suggest that it is unwise to edit an earlier reply that you have made, generally the OP will not notice. Best to add a new reply and note that it edits the previous one.