Synchronising and merging files doesn't work

Hi there,

since the newest version of premiere I've been using the sync option for my video and external audio files. I've never had a problem with it until today. When it runs through it it says something like (sorry translated from German): 'clips couldn't be synced because at least one out of your files didn't match.'

Has anyone experienced this before? I've tried to merge the files but there isn't even an error warning coming up. It simply doesn't do it.

Tipps anyone? Thank you!