Server 500 Error
This error is usually caused when the administrator of the Paper Tiger Online account has not created a database, at least 1 location in that database and at least 1 item prior to inviting users. When the invited user tries to sign in, this error occurs because the application doesn't know where to direct the user since the admin has not given the user access to the database(s), location(s) have not been set, or items have not been entered.
To correct this issue, the Admin on the account must make sure that at least 1 database, at least 1 location in that database and at least 1 item entered in that location has been initiated. Then reinvite the user including setting their permissions for the database/location.
Please refer to the article below for a step-by-step on how to do this. http://thepapertiger.com/support/articles.php?id=246912&catId=230