You cannot assign new users to project roles on the "Project Administration" EditProject.aspx web page if these users are not already members of another project.
I assume the issue is caused by the inner joins on the [BugNet_Roles] table in the [BugNet_User_GetUsersByProjectId] stored procedure, which will only return project users if they are already in the [BugNet_Roles] table. This probably will cause the subsequent insert failure on the [BugNet_UserRoles] table.
A workaround is to add the user to at least one project via "Manage Roles For This User" option on the EditUser.aspx web page, which is not affected by this issue.
I assume the issue is caused by the inner joins on the [BugNet_Roles] table in the [BugNet_User_GetUsersByProjectId] stored procedure, which will only return project users if they are already in the [BugNet_Roles] table. This probably will cause the subsequent insert failure on the [BugNet_UserRoles] table.
A workaround is to add the user to at least one project via "Manage Roles For This User" option on the EditUser.aspx web page, which is not affected by this issue.