Recently, some Google AdWords advertisers have been complaining in a WebmasterWorld thread that they were (1) being forced to upgrade to the MCC (My Client Center) section of the AdWords console and (2) after being upgraded, they lost their promotional credits in their accounts. That was reported late August.
On August 31st, in the afternoon, Google apparently emailed those affected by this with the promotional credit codes. One advertiser said, "I just got an email with the aforementioned credit codes." Some others also confirmed receiving such an email. The issue is, one advertiser said he tried the code and Google said they were not valid.
Google has yet to confirm or deny this possible bug.
Forum discussion at WebmasterWorld.

Comments:
David Rothwell
09/03/2009 11:01 am
My MCC has also been upgraded, with the loss of the promotional codes and data I had related to all those I've issued, so that is a nuisance. I was emailed 20 voucher codes in exchange, one of which I have used successfully. Trying to login to the new MCC last night kept crashing my browser session, so I guess they still have some bugs and operational issues to resolve in this whole area...
Béate Vervaecke
09/04/2009 04:55 pm
I lost my promotional credits as well (Belgium - Europe), but I still have to receive the first notice or vouchers by email. Google Arrogance...
Claire Jarrett
09/17/2009 02:18 pm
I cannot believe Google have done this, I have also lost all my vouchers. NO notification whatsoever, what a cheek!