files weren’t uploaded – files can’t be synced with SkyDrive

I constantly have problems with Office files (I'm running Office 365) that don't sync properly with SkyDrive. The files were created with various versions of Office apps. The error message tells me to open the file for more information, which is not forthcoming when I open the file. Sometimes, just by saving the file, the problem is resolved, sometimes not. It's very annoying since most of the files that become problematic are ones that I have not opened for weeks or months. Seemingly, the failure to sync is random. Short of going back to Dropbox, where this NEVER happened, how can I solve this problem?