Hello, thanks for becoming a VIP and donating to our cause.
I can see your status for VIP is done on main site: https://www.opensubtitles.org/en/profile/iduser-7246354
1: The 404 error may just be a temporary site issue.
2: There is also a slight lag between the main site and the new site whilst certain things get updated and transferred to the new site from this site. For some things it's one hour, for others, maybe even 24 hours or so.
3: Try it tomorrow, hopefully transferring your account should work by then. VIP status may not work immediately on the new site, as it's still in Beta testing. But all will be good before it goes live properly.
It does actually say:
"Enter the email used on opensubtitles.org, you will receive an email containing a link to create yourself a password on our new site. If previously activated, your VIP status will be migrated too."
You'd assume (by the above) VIP status should work immediately on the new site, but give it a day, and try again. It may just be the delay-lag.
And users should get an email when the site is fully functional.
If this doesn't resolve your issue by tomorrow, please use the "contact us" option from the bottom of the page from the main subtitle-site. A site programmer will be able to look into it for you.