I'm running Acronis True Image 2016 on my Win 10 Pro (X64) laptop as my backup solution. Whenever I run a backup, I get one or more "failed to backup file or folder" message which I can ignore or retry (the retry never works so I always ignore). It happens on different files almost every time. This morning, for example, it failed to backup a .PDF. There were probably more that failed but I chose to "ignore all". This can happen the backup runs on a scheduled basis (in which case, the backup simply fails) or it can happen when I run it manually. I'm not sure if it is happening on full backups but do know that it happens on incremental backups.
One of the odd things about this is that I ran two backups this morning. The source folders and files were the same but the destination drives / folders were different. The error popped up on the first run but did not popup on the second.