FMC Message "AHRS Input Fail"

Hi all,
First off, let me say how much I'm enjoying this aircraft, simply wonderful.
 

Recently, after loading the aircraft and powering the FMC it's giving the message "AHRS Input Fail" after I click "accept" and then click the flightplan button. I don't recall this happening in the first couple of days.

It has also given another message from time to time relating to RAIM, however I can't recall the exact message.
 

I'd appreciate any assistance in relation to this.