Probably because your web connection is down. When the connection becomes available again, it synchronizes all pending orders so that you do not loose data.

The suggested solution doesn't seem to work at all. Can you elaborate on the solution?

We've seen that if the red button shows up you should clean your cookies and it will work again.

We were doing many tests and changing ways of selling (i.e. normal and pos) and for some reason information in cookies prevents you to do a normal POS.

Juan Pablo