Walker and brakewoman Gillian Cooke appeared well placed to finish in the top three after producing the third best time of run one in Germany only for it to go disastrously wrong in run two.
The British duo improved their start by four hundredths of a second but were to fall from third overall to last after crashing during the second run as the Altenberg track appeared to slow.
Had Walker and Cooke finished in the top-three it would have been the best performance by a British women's sled for four years and the pilot's best since making her World Cup debut in 2009.
As it was they finished 13th, clocking 58.53 seconds in run one and 1:05.01 minutes in run two for a combined time of 2:03.54, 6.59 seconds behind winner Cathleen Martini of Germany.
Martini got the better of Humphries by 0.25 after the first run after clocking 58.10 to place first to her second and, despite failing to match that second time out, she took victory in 1:56.95.
Walker wasn't the only one to struggle though as Humphries fell from second to third after going over half a second slower on run two to end her unbeaten run in this season’s World Cup.
Humphries also took the final two World Cup wins last season and the World Championship title but had to make do with third in Altenberg 0.02 behind Sandra Kiriasis who was 0.30 adrift of Martini in second.