SetValueBool

This is driving me crazy.
it works,
then it doesn't,
then it works
now it doesn't again.

How the heck do you use the method SetValueBool( ) in IMyTerminalBlock? I have tried using it as
block.SetValueBool( "ShowOnHUD", true ); (which used to work, then not...l then did again.. then... yeah you get the idea)
And I tried using it as a static method IMyTerminalBlock.SetValueBool( block, "ShowOnHUD", true );
But in both cases I get an error about a variable not being instantiated however the...

SetValueBool