Hello,
As per the earlier thread:
http://groups.google.com/group/adwords-api/browse_thread/thread/2f3fc07d2854d585/f033ce563c6b48a2
the Sandbox is currently having trouble accepting requests. I believe
that the currency code errors are a different manifestation of the
earlier "internal errors" that were being returned.
I have a feeling that this is going to be resolved by performing a
refresh of the Sandbox's backend data servers, but that hasn't taken
place yet. Apologies for the downtime in the meantime.
Cheers,
-Jeff Posnick, AdWords API Team