Without any exact info nobody can help you. Version of AE, version of C4D, versions of the import plug-in, details about the files, whether they were saved with Melange compatibility and al lthat good stuff.
Adobe CS6, Cinema4D r14, worked flawlessly before, now i can't import a .c4d file.
You don't import a C4D file with those versions; you import an AEC file. You create that by going to your render settings in C4D, under the Save section, under Compositing Project file. Make sure it's set for After Effects, and Include 3d Data is checked. Then click "Save Project File..."
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