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This can occur if After Effects is failing to communicate with the QuickTime server because the communication is blocked---usually by overly aggressive firewall settings.
See this document:
Still same thing "/
Try starting the operating system in Safe mode and then starting After Effects.
Generic permission issues perhaps? UAC? Impossibel to tell. I suggest you download Sysinternals' Process Monitor and set it to filter on the Quicktime service executable that is launched with AE and then see where it is unable to access files or specific Registry keys... This should at least provide a clue as to what's going on...