We're really sorry if you are receiving 'Threshold/Selection is not available' error messages when working with your actions.
These error messages can appear for a number of reasons, and essentially mean that your Photoshop is currently unable to recognise your specific layer or tool, in order to follow a specific part of the instructions, laid out within these actions.
Actions are rather language-specific tools, so you will need to ensure that you are working in the English version of Photoshop, unless specified otherwise by the designer.
As actions are essentially a set of instructions, that you run on your image, it is really important that your layers in the PSD file (if applicable) are labelled as specified by the designer. When you receive a threshold error message, this usually means that your actions are unable to recognise your image layer, to be able to run the action properly.
If you ensure that you are selecting your image layer before playing your action, and that you have not changed the layer name in any way, this should be able to work for you.