[Q] E:Can't mount /sdcard! ( Help me ) ?

Prestigio - PMP7280C3G V4.2.2

I'm in ( rua1 CWM v5.5.0.4 for PMP7280C3G V4.2.2 )

I got to the part where I need to install SuperSU-v1.65.zip it has options such as this one ( install zip from sdcard ) so I click the Tablet power button to choose it then from there I choose ( apply /sdcard/update.zip ) then it says...

-- installing: /sdcard/update.zip
Finding update package...
E:Can't mount /sdcard/update.zip

Please does anyone know what I need to do.

Any Helpful Steps on things to check and do and any Information will be much and greatly Appreciated.

Also I posted this Question on another website someone replied and said to rename the SuperSU-v1.65.zip to update.zip I have and nothing still works it's still Can't mount.

Here's a picture I recently took of the screen.