wlanapi.dll throws exception in rpc thread

When unregistering my callback:

::WlanRegisterNotification
(m_hClient,
WLAN_NOTIFICATION_SOURCE_NONE,
FALSE /* don't ignore duplicates */,
NULL,
NULL,
NULL /* reserved, must be NULL */,
NULL);

an exception is thrown from an RPC thread which includes wlanapi.dll in
the callstack. The exception is something like: "0x0000000D The data
is invalid". I'd expect that this error be returned from the
WLanRegisterNotification call, but that is returning 0.
The thread from whcih I make the WlanRegisterNotification call is
waiting for an sync. event object when this exception is thrown from
another thread.

Has anyone seen this before or know the cause?

My handle value (m_hClient) appears to be valid.

joshl@purenetworks.com