PNG not working for a WORDPRESS

Hi.
I am working with ILLUSTRATOR making a simple logo and after passing them to PHOTOSHOP, I want to save it in .PNG format so that it has a transparent background. everything works fine apparently stopping it when uploading it to WP gives me error of "file not allowed for security reasons".
If I upload other files created previously if I can.
It also happens to me with the .JPEG format.
Any ideas about it?
Thank you.