Problem uploading a new media file

Hi
I am running a vantage premium theme (version 2.2.3) and access my site via a mac mini running OSX Yosemite Version 10.10.4. I am ok changing things on my word press sites, but new to cpanel…
Uploading a file I get “[an error occurred while processing this directive]
Alerta de seguridad

El archivo que intenta subir ha sido rechazado por el servidor.
Probablemente contenga virus o troyanos que pueden da?ar su sitio web.

No intente subirlo nuevamente, ya que su dirección IP podrá ser bloqueada.”

I have run a virus scan, and no errors are shown on my mac. i also run one via cpanel (not sure how good this is). Nothing found.

I have not recently added any plug ins, and a couple of days ago added 3 media pictures to my website. Todays picture was a screenshot.

I am not sure where to go next… any advice welcome