[Error] - SubSystem block does not have a parameter named 'u'

I have a simple simulink model,

1. two states - On and OFF
2. one output - y, attached to a scope
3. one parameter - u
4. transition rules - when u < 0 goto OFF, when u > 0 go to ON

I'm trying to do the following from the workspace,

set_param ('Model/Block','u','1')

and I'm getting 'subsystem block does not have a parameter named 'u''...all I want to do is to toggle the parameter 'u' from 0 to 1 and 1 to 0 to observe the effect on the scope..

Can someone plz point out where I have gone wrong?

Many thanks, Luke

[A Jenkins]

Can you be more clear about what kind of parameter 'u' is? Is it a constant block? A mask parameter? A parameter in the model workspace?

Try

get_param('Model/Block', 'ObjectParameters')

to see what you are allowed to set.