Chart no longer detected



After 6 months of operating with a navionics vector WVNAU62MAP5.1 chart it suddenly disappeared. Everything was operating fine at the time and while I was watching the screen the detailed navionics contours, islands etc vanished. Nothing was been touched on the screen and no settings, menus were open at the time, just the plotter and sounder. Restarting does not help. In checking current settings I have:
The 2nd SD card is clean and installed correctly
The Menu initial setup Charts Master Device is ON
There is no Master chart undetected warning on startup
Home- Catalogue - My Charts shows no chart and All Detected Charts shows no charts

Please help
Also Rotokey- Chart - is set on 'Auto' and
Menu - Plotter Display - Chart Priority in Auto Mode gives an option of only Vector or Raster and is set on 'Vector'
Sounds like one of the chart cards are not seated correctly. Remove what you have from BOTH SD card slots and reseat them.
Hi Johnny
I tried the removal and reseat advice but this did not make any difference. Also when I tried to backup/export my waypoints via Menu-Files-Export, neither of the left or right SD cards were shown highlighted. (I tried this after reseating them)
By the sound of it, the unit has either a card reader problem or other internal issue. It is time to contact your local dealer or send the unit into your local distributors service center.