Need help for model deplacement

[Anonymous]

Goodafternoon,

I'm working on a project where I have to calcul a frame to lift modul.

It's a steel frame on what I but my timber structure.

So I made the model that you can fine in attachment, but I don't understand something:

I do not have any X reaction, so it means that I'm a the gravity center of the structure, but I have an understandable deplacement.

I do not have any instability, so I really have a problem to understand where I made a mistake.

Is there someone who knows why I have this deplacement ?

Thank you for helping.

(And sorry for my English ...)

[Rafal.Gaweda]

It is a mechanism - red bars below are truss bars ; structure can easily rotate around axis of bar 120

Skyline solver reports instability