Flat-Pattern and sheet metal creating complains about "edges to be ripped..."
-> No Flat-Pattern created therefore.
The problem corner is in [picture 1] below and it needs to be "more open"...
Edge rip is used to split a face that has no edge at all - so if the lower flange was not disconnected (at red line) edge rip could be used to create that split.
If you want a gap, then Normal Cutout is a better option than extrude as the edge face will be perpendicular to the sheet faces and create the correct edge for flat pattern. One method is to unbend-cutout-rebend as shown below.
like dave is telling is that the edge rip is use to split faces.
In this feature you can split corner edges (here you can select the edges)
for faces that needs to split you need to create curves for where the split needs to come.
in you use the convert to sheetmetal wizard you see at the step edge rip the options:
Select edge (existion edges)
Select section (curves)
in the added movie you see what this is doing.