sometimes the small metal dog leg to the top right of the bobbin holder section will come out this normaly happens if the threead has been pulled hard. the thread then keeps catching on it and you cannot sew. so here is the solution to that problem. remove the foor plate the bobbin case holder and the bobbin case itself. as normal for cleaning.

next look to the left of he bobbin case holder and you will see a silver piece of metal. carefully push this towards the right hand side, yes its suposed to be moved. this is what holds the dog leg inplace. replace the dog leg and slide the metal piece back into its correct positon on the right hand side the dog leg bit of metal is once more secured
next if you keep getting the message to remove the thread jam time and again then once more remove the bobbin as if for cleaning and again gently ease the piece of metal on the left hand side towards the right, this will allow you to lift up the thread cutterinto an vertical positiuon and yo can totaly clear away and bits of thread or dust that has collected onto the black plastic hook and loop stuff that holds the threads. put the blade cutter back to its original position and once more return the metal bar to its left hand place. if yo have a problem undestanding this PM me and i wil send you a picture .
i hope this will save you time and money in repair bills and a lot of frustration and lost work.
annie in the uk http://groups.yahoo.com/group/craftingaroundtheworld/