"Unexpected symbol" often means missing punctuation.
In this case, it looks like
panel=function(){panel.xyplot(Kalibrierung$Spannung,Kalibrierung
$Magnetfeld)panel.abline(reg=test)}
this argument is missing a semi-colon ";" before "panel.abline".
panel=function(){panel.xyplot(Kalibrierung$Spannung,Kalibrierung
$Magnetfeld); panel.abline(reg=test)}