Vertex not working.

Hello can someone help me i amusing vertex to edit a corner to make it rounded off and for some reason an invisible box has appeared and it is stopping me from using the vertex tool, this might be a stupid question but its my first map so bear with me :p can anyone help me fix this?

Fixed now by restarting hammer, any other ways to do this?

It sounds to me like you accidentally started the vertex selector.

When vertex editing you can drag a box with the mouse over the vertices you want instead of selecting them individually, then press enter to select them.

This box will stay there and prevent you from selecting individual vertices until you press the enter key to finish selecting.

PS: Clip tool for curves