Each submission passes through an automatic spam check, and there are a number of reasons why your submission may have been flagged as potential spam. For instance, perhaps you submitted a blank document or a document that appears to have been plagiarised.
Please note: Having your submission flagged as spam will not necessarily reflect poorly on you with employers, and you are able to re-submit your work if it is flagged as a potential spam submission. To do so, you can select 'Re-submit Task' to override your previous submission.