There are two possible causes:
Incorrect file format. Check that your file is in one of the following formats: pdf, jpg, jpeg, png, txt, doc, docx, doc, tif, tiff, xlsx, xls, pptx, ppt, png, gif, bmp, mov, mp3, mp4, m4v, avi, wmv, mpg, psd, wav, m4a, wma, aac, or zip;
File size (MB) exceeded. Check the maximum size of the files you want to upload. You can add one or more files up to a maximum of 100 MB.
If you are still unable to upload files, please contact our Information Centre.