Problems automatically uploading

I have a skydrive account that is set up to automatically sync and upload documents from my hard drive when any changes are made - acting as an online backup.  This worked for a few months but recently the system has stopped uploading pdfs, autocad files, jpegs etc.  It does still sync and upload microsoft office files.  I have office 365 and skydrive is part of that package.  Also I am working on windows 7.