This is what I have tried.
1. I have created an new email account before delete ".ispconfig_lock" file, then right away, I tried to login to the webmail using this new email account. It failed
2. I deleted ".ispconfig_lock", tried right away to login via the webmail. It works
3. I tried to create another email account, then tried to login via the webmail. It failed again.
any idea? thank you in advance!!!