I was having the same problem, and got it to work by replacing this in includes/modules/shipping/usps.php:
$this->types = array('EXPRESS' => 'Express Mail',
'FIRST CLASS' => 'First-Class Mail',
'PRIORITY' => 'Priority Mail',
'PARCEL' => 'Parcel Post');
$this->intl_types = array('GLOBAL EXPRESS' => 'Global Express Guaranteed',
'GLOBAL EXPRESS NON-DOC RECT' => 'Global Express Guaranteed Non-Document Rectangular',
'GLOBAL EXPRESS NON-DOC NON-RECT' => 'Global Express Guaranteed Non-Document Non-Rectangular',
'EXPRESS MAIL INT' => 'Express Mail International (EMS)',
'EXPRESS MAIL INT FLAT RATE ENV' => 'Express Mail International (EMS) Flat Rate Envelope',
'PRIORITY MAIL INT' => 'Priority Mail International',
'PRIORITY MAIL INT FLAT RATE ENV' => 'Priority Mail International Flat Rate Envelope',
'PRIORITY MAIL INT FLAT RATE BOX' => 'Priority Mail International Flat Rate Box',
'FIRST-CLASS MAIL INT' => 'First-Class Mail International');
with this:
$this->types = array('EXPRESS' => 'Express Mail',
'FIRST CLASS' => 'First-Class Mail',
'PRIORITY' => 'Priority Mail',
'PARCEL' => 'Parcel Post',
'MEDIA' => 'Media Mail',
'BPM' => 'Bound Printed Material',
'LIBRARY' => 'Library'
);
$this->intl_types = array(
'Global Express' => 'Global Express Guaranteed',
'Global Express Non-Doc Rect' => 'Global Express Guaranteed Non-Document Rectangular',
'Global Express Non-Doc Non-Rect' => 'Global Express Guaranteed Non-Document Non-Rectangular',
'Global Express Envelopes' => 'USPS GXG Envelopes',
'Express Mail Int' => 'Express Mail International (EMS)',
'Express Mail Int Flat Rate Env' => 'Express Mail International (EMS) Flat-Rate Envelope',
'Priority Mail International' => 'Priority Mail International',
'Priority Mail Int Flat Rate Env' => 'Priority Mail International Flat-Rate Envelope',
'Priority Mail Int Flat Rate Box' => 'Priority Mail International Flat-Rate Box',
'Priority Mail Int Flat Rate Lrg Box' => 'Priority Mail International Large Flat Rate Box',
'First Class Mail Int Lrg Env' => 'First Class Mail International Large Envelope',
'First Class Mail Int Package' => 'First Class Mail International Package',
'First Class Mail Int Letters' => 'First Class Mail International Letters',
'First Class Mail Int Flats' => 'First Class Mail International Flats',
'First Class Mail Int Parcels' => 'First Class Mail International Parcels'
);
Hope that helps.