[Gate-users] Simle GATE example

[Nouf Abuhadi]

Hi,
 
I am a new user in GATE. I tried to do an example as in the user guide V6.1.
I tried to do the first step which is defining a scanner geometry when I did the visualization, then I add the world volume it is ok but I got an error 

#  S Y S T E M
Idle> /gate/world/daughters/name cylindricalPET
Idle> /gate/world/daughters/insert cylinder
Idle> /gate/cylindricalPET/setMaterial Water
src/GateMaterialDatabase.cc (l.126): GateMaterialDatabase: could not find the definition for material 'Water' in material files
 
Could someone tell me Why this error appear? please.
and How can I run a simple example?
 
Regards,