HUGS display empty

After the runway elevation + runway length have been set (as per the tuto1 pages 71&72) the HUGS controller reads : mode PRISTBY IMC A IIIRWY E 0'GS -3.00° but the HUGS symbology that should show A III approach mode, does not show up when fully established on the ILS 18R EHAM (ILS freq 110.10 in both left and right NAV radios and course set to 184° in both course selectors). I tried 3 or 4 times but the display stays empty all the times I didn't make any change in the FMC (PMDG/Aircraft/Equipment), the HUGS auto AIII mode is still set to YES What do I do wrong ? What do I miss ? Can I check the HGS while on the ground ? If yes, do I need to position the a/c on the runway for example the 18R EHAM to check it ? or can I try it anywhere on the airfield ? Any information would be greatly appreciated Merci