PS I also tried
start = list( fixef = c( -9.28405, 2.81300, -4.75935, 2.91080),
ST = c(0, 8.29931, 2.56368e-06, 0.00000))
and
start = list( fixef = list( -9.28405, 2.81300, -4.75935, 2.91080),
ST = list(0, 8.29931, 2.56368e-06, 0.00000))
to no avail.