In fact, the metamagic you ned to pass throught Ward by copying someones aura, you need Flexible signature metamagic, not masking (Masking only works to hide your magic level, but against ward it is ineffective..)
Reread Street magic
"Only magicians with the
Masking metamagic technique
(p. 190, SR4) or spirits with the Aura Masking
power (p. 98) may attempt to synchronize their aura with
a ward in such a way. In order to synchronize one’s aura so
it mimics a ward’s creator, the synchronizing magician or
spirit must be able to see the creator’s aura to use as a reference.
One way to do this is to track the astral link present
between a ward and its creator (see Astral Tracking, p. 185,
SR4). Then an Opposed Test is made between the initiate’s
Intuition + Magic + initiate grade and the ward’s Force x
2. If the intruding magician succeeds, the ward no longer
inhibits them. If the ward wins, it continues to inhibit the
intruding magician, but does not alert its creator until the
intruding magician tries to force his way through by another
method."