getting "failed to create cart" when adding non-amazon related product to Ubercart shopping cart

This seems like a strange error to get, but when using Ubercart to add product nodes to a shopping cart, Amazon returns an error saying "failed to build cart." I assumed it was a UC issue until I looked at the log, and Amazon is throwing this error when I'm using UC:

Amazon error returned. Code=AWS.ParameterOutOfRange, Message=The value you specified for Quantity is invalid. Valid values must be between 1 and 999. // ///SimpleXMLElement Object ( [OperationRequest] => SimpleXMLElement Object ( [HTTPHeaders] => SimpleXMLElement Object ( [Header] => SimpleXMLElement Object ( [@attributes] => Array ( [Name] => UserAgent [Value] => Drupal (+http://drupal.org/) ) ) ) [RequestId] => 1CNN0RZT6JPQ452E19JC [Arguments] => SimpleXMLElement Object ( [Argument] => Array ( [0] => SimpleXMLElement Object ( [@attributes] => Array ( [Name] => AssociateTag [Value] => porterworks-20 ) ) [1] => SimpleXMLElement Object ( [@attributes] => Array ( [Name] => Service [Value] => AWSECommerceService ) ) [2] => SimpleXMLElement Object ( [@attributes] => Array ( [Name] => Signature [Value] => 7Msu2IXjoiO0FeTS7C6UTMNnh4ubSLpt2RMrogB0tqw= ) ) [3] => SimpleXMLElement Object ( [@attributes] => Array ( [Name] => Item.1.OfferListingId [Value] => 1 ) ) [4] => SimpleXMLElement Object ( [@attributes] => Array ( [Name] => Item.1.Quantity [Value] => 0,uc_product ) ) [5] => SimpleXMLElement Object ( [@attributes] => Array ( [Name] => HMAC ) ) [6] => SimpleXMLElement Object ( [@attributes] => Array ( [Name] => Operation [Value] => CartCreate ) ) [7] => SimpleXMLElement Object ( [@attributes] => Array ( [Name] => CartId ) ) [8] => SimpleXMLElement Object ( [@attributes] => Array ( [Name] => OfferListingId [Value] => 1 ) ) [9] => SimpleXMLElement Object ( [@attributes] => Array ( [Name] => AWSAccessKeyId [Value] => AKIAJ5LX4NHEZWVZWLCQ ) ) [10] => SimpleXMLElement Object ( [@attributes] => Array ( [Name] => Version [Value] => 2009-03-31 ) ) [11] => SimpleXMLElement Object ( [@attributes] => Array ( [Name] => Timestamp [Value] => 2009-08-07T02:07:36Z ) ) [12] => SimpleXMLElement Object ( [@attributes] => Array ( [Name] => MergeCart [Value] => True ) ) ) ) [RequestProcessingTime] => 0.00365781784057617 ) [Cart] => SimpleXMLElement Object ( [Request] => SimpleXMLElement Object ( [IsValid] => False [CartCreateRequest] => SimpleXMLElement Object ( [MergeCart] => True [Items] => SimpleXMLElement Object ( [Item] => SimpleXMLElement Object ( [OfferListingId] => 1 [Quantity] => 0,uc_product ) ) ) [Errors] => SimpleXMLElement Object ( [Error] => SimpleXMLElement Object ( [Code] => AWS.ParameterOutOfRange [Message] => The value you specified for Quantity is invalid. Valid values must be between 1 and 999. ) ) ) ) )

is there a way to make these two modules play nice together?