Hi Zlata! This is very strange... I'm not quite sure what the problem could be. Do you have installed the latest version of Grasshopper (0.9.0076)? Go to Help > About... to see the version or build. This is a long shot but are you sure it is the "normal" x from your keyboard? not like (x, ×, X, ✕, ☓, ✖, ✗, ✘) or something similar?. What happens if you use "N" or "n" instead of "x" as the variable, does that work? Let me know, Cheers! Arie