The issue as to whether the tax lien was the "fault" of the consumer needs to be addressed with the furnisher of that information to the CRA.
Tax liens, unlike other reported adverse items, do not have a CR exclusion date based on the date of occurence of the adverse item itself, but rather a 7 year period that begins on the date paid. So it has a while to run.
If it was not your responsibility, then you can send a direct dispute to the furnisher, questioning the accuracy of their reporting.
If they verify, then you would have to pursue the dispute via other means, such as civil action, where you can get all the evidence considered by a third party.
If deletion based on inaccuracy of reporting cannot be obtained, you are left with asking the furnisher to delete based on their good-will.
I don't think it matters when it was paid. It only matters that the lien was issued which makes it factual. That being said, I recently went through almost the same scenario. A state tax lien was filed against my husband that did to belong to him. The state's attorney went to court and had it vacated by the judge. The court order he gave me says " filed in error." I guess it is still on his CR for now but the state's atty said he will have it removed. You could try that route. It worked for me.