Hello,
I thought you had 2.0.0-beta4 before. Versions 1.5.9 and 2.0.0 are not compatible and there can be problem with update. We never tested it, because we never planned to make them compatible. But there can be problem only in database and I don't think this problem can be caused by it.
I have no problem with week calendar if I am logged in. Also problem from error has no sense, because same code is used also in month calendar.
Can you send us ftp to
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so we can check it?