Reason 1: You are trying to upload a folder using drag and drop.
Solution: Upload of folders via drag & drop is only supported by the following browsers:
- Google Chrome
- Firefox (from version 52)
- Opera (from version 43)
- Microsoft Edge (from Windows 10 anniversary update)
Reason 2: You are trying to upload data from an external source (e.g. iPhone, OneDrive).
Solution: Copy the data to your computer first, then upload to myCloud.