Hello DanNo, I did not receive an automated response. Looks like my mail or the response gets stuck somewhere. I use my email address (ico[at]ico.ch) for online shopping with PMDG since February 2006 and never had any issues.But something has changed because I installed the MD-11 flawlessly on on the same PC last November. I thought it could perhaps has to do something with Windows Vista and decided to test it and deinstalled the MD-11 on the harddisk which runs Windows XP, yesterday. Now the validation fails there too, obviously this is not a Windows Vista specific problem and yes I have disabled the firewall, uac and so on.Interestingly the validation of the PMDG 747 (same email address and password) worked perfect. (@Ralph - I changed the password to a 8-digit one, even checked one with 5 digits, tried more than twice but it did not help).Kind of mad that it works with the 747 and fails on the MD-11. Can the support team make investigations what causes this headache. Thanks in advance. Best,RolfSOLUTION - SOLUTION - SOLUTION -->The validation fails on the original installer for FSX, released October 14, 2008 but works with the combo installer released January 6, 2009. This really did drive me nuts %P<-- SOLUTION - SOLUTION - SOLUTION