[Serusers] Subscription Error

Hi, Here is my problem in user subscription using serweb: 1st phenomenon: I use User Management Page to add a user by means of Subscription. After I have added a user with username "thomas", and after receiving the confirmation email and clicking on the provided link, the error message occurs: "400 Table 'aliases' not found in memory, use save("aliases") or lookup("aliases") in the configuration script first We regret but your officehk123.vttsys.com confirmation attempt failed. Please contact info(a)iptel.org for further assistance." However, I can login the user management page using "thomas". Question: - What is the cause of such error? - Why could I login the User Management Page? 2nd phenomenon: I go to the AdminLogin page to delete the user "thomas". The user account is removed from the table. However, strange thing happens. When I go to the User Management Subscription page to add a user "thomas", error message displays: Sorry, the user name 'thomas' has already been chosen. Try again. Question: - user "thomas" is supposed to be deleted. However, I am not allowed to add it again. Why does this happen? Anyone can help me? Thank you very much. Thomas