As I advised in class and here on the blog – turnitin can provide some difficulty when uploading large files. It is suggested that you follow the advice provided by the library on the turnitin FAQ page
“The file size may not exceed 20 MB. It may be necessary to compress a document so it is small enough to be uploaded to Turnitin. This is especially true for long documents (such as dissertations) or documents that contain many images.
Saving Word documents to PDF format will often compress the document to a small size; however PDF documents must contain text to be submitted. PDF files containing only images of text will be rejected during the upload attempt.
To compress or minimise the file size of a document with many images:
• Right-click on any picture in your document and select Format Picture from the shortcut menu.
• From the Picture Tool toolbar, click on the ‘Compress Pictures’ icon
• When the dialog window opens, select ‘Apply to all pictures’ and click OK.
For further assistance, please contact the Turnitin Officer”
Hope this helps.