How can I fix my Jura impressa S9 coffee machine?

The display flashes FILL SYSTEM/PRESS STEAM. When the steam button is pressed the machine makes grinding and pumping sounds then the above message appears again. This happens with out fail. I have tried emptying the water tank, removing the water tank, varying levels of water all to no avail. According to the online manual this message is due to no water in the tank (see above), an ill fitted filter (we don't use filters) or the tank fitted incorrectly. Switching the machine off at the wall doesn't reset it please help me.

Sarah
January 2006