Hi Johan,
I'm not sure if you have a question or not.
According to the release notes, in 6.45 the _popupdone property was renamed to popupdone.
And as far as I can see all the references in the Templates and Classes refer to popupDone not _popupDone.
You don't mention which build you were upgrading from, and you don't mention if you are seeing this error in embed code, or generated code, but it sounds like maybe it's in generated code.
If so you might want to unregister and then re-register the template. It sounds like you're using the latest class, but perhaps with an old template.
cheers
Bruce