Hi,
Try to reinstall the software on the FP controller, if you are running Fieldpoint 3.0.2 you can browse for the controller in the subnet, once Fieldpoint explorer find it you can right-click on the controller and choose the option Install/Update Software.
Fieldpoint explorer will ask you if you want uninstall the current software and you should choose Yes.
After that try to target to the controller again.
Regards
Andre Oliveira