The following error explanation was reported. E099, System error or invalid input when installing a license string. This message has been reported by a number of partners that have been given valid license strings.
The E099 error is a catchall error code. There are codes for licenses that are already used and invalid license keys so this is somewhat unique. I checked the logs on the and do see on several days the E099 errors. Please confirm that these are licenses for the XAS 2.0 Apps (Dropbox, Office 365, and Print from URL), the XAS 1.0 app licenses are not valid any more.
I would suggest moving this discussion to the feedback email since I believe we'll need the license keys you are using to determine the cause of the issue. If you could include a license key and a specific account that the error is occuring on that would be helpful as well.
The Xerox license server was unable to communicate properly with the Xerox App Studio licensing system from January 23rd through 26th, 2015. If you attempted to enter a valid license during that period you would of received an E099 error. Your licenses are still valid and can be re-entered into Xerox App Studio now.