Error while trying to use Autopilot for Testers

Hello,

I try to run the code generated from Autopilot. For a simple login it’s working, but when I try something different like checking if a button exists, I get different errors like :Unexpected error has occurred during the library compilation process:
The assembly compilation returned the following errors:

*Validate ‘NEW CONTACT’ button click functionality.cs(39,49): error CS1061: ‘UiTargetApp’ does not contain a definition for ‘PathExists’ and no accessible extension method ‘PathExists’ accepting a first argument of type ‘UiTargetApp’ could be found (are you missing a using directive or an assembly reference?)
button click functionality.cs(44,47): error CS1061: ‘UiTargetApp’ does not contain a definition for ‘PathExists’ and no accessible extension method ‘PathExists’ accepting a first argument of type ‘UiTargetApp’ could be found (are you missing a using directive or an assembly reference?)

Do you have any ideas if I have to install something ?

Thanks in advance!