It is not invalid until you bring a legal action to have it declared invalid and removed. Until then, it will remain on your property. You can file the legal action to remove it yourself, but it is not necessarily easy for a nonlawyer. However, if you can't afford a lawyer, you are allowed to file it "pro se" (as your own attorney): contact your country court's clerk's office for instructions and go to the court's website (where they likely have the court rules and possibly sample or template forms). You can also sue the individual who put the lien on  for "abuse of process" or "malicious use of process" (terms vary), for filing a groundless lien, to recover compensation for any costs or losses (like the profit from a lost sale) you can show occured due to this lien. Before doing so, a good idea may be to contact the individual and let him know that you will be suing him if he will not remove the lien--that may inspire him to voluntarily remove it, and, if you not, you can still bring your legal action.