How to control servo with scratch?


I start in scratch and I find myself in front of a problem.
I have a gopigo 3. I use scratch for robots, software provided by dexter.

The first data sent to gopigo is
“broadcast servo 1 45”
The servo moves well at 45 degrees

then when I change the value, the log writes:

[quote] GoPiGo3 Scratch: Error is instance () arg 2 must be class, type, or tuple of classes and types
[/ Quote]
and the servo does not move anymore.

I am blocked.

thank you in advance