I note that you typed that you removed the battery from the car, which also removes it from any possible circuit losses that the car might have and which may be less than obvious..?
While the battery may be suffering increased internal losses due to the ageing processes, if the car circuitry may also be added to the demands placed on the charger, perhaps the combination of both may have just exceeded your chargers capability to bring it up to the required state of charge, and thus causing the charger to produce fault indication...?
