This problem now seems to have something to do with an unfinalised A&D obect existing when the unit reboots.
This can happen, for example, when a download was started, but failed to complete.
But why should this cause all subsequent adl_smsSend calls to fail?
Actually, it seems that the presence of any A&D obect (finalised or not) can cause this - I have now seen it happen after a successful DOTA firmware update!
If my application detects the presence of any A&D obect at startup, it formats the A&D volume.
The ADL User Guide doesn’t state any restrictions on calling adl_adFormat - but should I wait for any particular WIND events?
Should I always reboot after an adl_adFormat?