Just a heads-up, but I had a complete failure of Dynamic Link today between AE and PPro (in either direction), and spent a long while discussing with customer and tech support, with no solution forthcoming.
To all intents, it looked like a corruption of the Dynamic Link DLLs or similar code, and as a side-effect, QuickTime dependent files were also failing to play (I'm on a PC system). The errors I received all centered around Dynamic Link not being able to start when I tried to import PPro into AE or AE into PPro, either via the 'File > Adobe Dynamic Link' menu, via 'Import' or concerning AE comps already on a PPro timeline. Attempting to re-link media in PPro also failed (though without any errors).
I tried numerous fixes, including de/re-activating, multiple restarts, internet disconnection, etc, but to no avail and was about to try a full reinstall.
However, and by chance, I found the culprit to be a malware app that installs silently (no idea how mine was installed) and is frequently not detected by spyware/anti-virus tools. The offending malware is called RelevantKnowledge, and installs as a DLL to track browser activity. On a Windows system, you may see a small globe-type icon in your system tray indicating its presence, but sometimes (I gather) this is hidden. Standard add/remove via Windows doesn't remove the app, only the entry, and it must be manually removed from 'Program Files', though some DLLs and the folder will not remove until you reboot. You may also have to check that the silently installed add-on in Firefox (etc) has been disabled, so more than one restart may be required.
Once removed, Dynamic Link was back, as was QT playback. Obviously, reinstalling (which was tech support's suggestion), would not have had any effect even if I had taken that course of action, as I believe the malware works by blocking some TCP/IP ports that Dynamic Link utilises (I may be wrong, but this seems to be the only explicable cause).
Hopefully this issue won't affect any of you, but please do check this if you get any Dynamic Link weirdness, and don't lose a day like I have just done, or worse still, hope that reinstalling will fix things!