Using Premiere Pro 14.0 and getting an error-log of hundreds of these errors (Player:11). Working from MOV and MP4 files generated from Canon DSLRs. It has been bad enough to crash Premiere several times. Not willing to run off software, using all Adobe certified hardware, and running off an external HDD (doesn't make a difference if working locally).
Some also get around the issue by changing the renderer in Project Settings > General to "Software Only" for the Mercury Playback Engine. Hope it helps those folks experiencing the issue. Unfortunately, you no longer have access to GPU acceleration when you do that. In that case, it would be good to look at system requirements to verify if your GPU is powerful enough.