Lien on builder prior to sale, creditors threat to now lien me

[Sendil Thangavelu]

Hello, recently i purchased a new construction from a large builder and we went through closing and such as part of the buying. Several weeks after sale,  out of the blue I received a letter form a creditor that there was a lien for $600 on the property PRIOR to the sale, that the builder never paid and now they are going to put a lien on the property against my name. IS this even legal?  I have written to the builder asking them to cure this issue, but I must say that this builder has been very difficult to get anything done. Am i really liable for this payment? I closed the property in March, creditor in their letter to me say that they had a lien on the property in February. I wonder how the closing process was completed when there was a lien on the property? Any guidance is appreciated. 

Thank you in advance.

Sendil