How to Clear "Please Clean CTD Sensor" Message on 5100 CN?

I really did read the FAQ's before I posted this - but if I missed it in there, please forgive me.

 

This message popped up today and I followed the directions in the manual to clean the little window.  I closed the printer - plugged it back in and it still reads "Please Clean CTD Sensor"

 

Help - what do I do  now.?

 

Thanks

 

Denise