eBay linked to a message from Andale's Senior Vice President of Customer Operations, who said the issue was due to a bug in the vendor software it utilizes for its database (http://corp.andale.com/x-outage.html).
On Tuesday evening, eBay updated its announcement and offered sellers advice on communicating with buyers, and it pointed sellers to its own listing tools "to list items while Andale's service remains unavailable" (http://www2.ebay.com/aw/core/200511011831421.html).