Hi, I have been using Zoiper happily for about 2 years but now it's giving some trouble. When I try to make an 'ordinary' moblie phone call (to masts of phone company) Zoiper comes on the screen (covering the normal mobile call screen) for one second and the call drops from the phone screen (red phone icon turns green again ... call dropped and a Zoiper message appears in a small window near the bottom of the screen saying: "Zoiper changed sound to silent. You can manually adjust the sound...". So, now I can't make any ordinary mobile calls at all. Any help please? Greatfully appreciated.