It is amazing how so many people go into business for themselves without realizing the full extent of the liability they are taking on by signing a long term leases. The situation you describe happens over and over again.
Presumably, you signed a long term lease that personally obligated you (and anyone else who signed the lease) for all rent payments due over the term of the lease. You may have then sold the business and, no doubt, had the new owner take over the lease payments. Or, you may have subleased the property from the previous owners and signed a document in the process that made you liable to the landlord, as well.
Likewise, the landlord probably accepted rent payments from the new owner, but if your name was still on the lease, you are probably still liable for the rent payments if your buyer fails to make them. The landlord would have a duty to mitigate his damages by, for example, reletting the premises. But the original tenants or previous subtenants, including yourself, could be left holding the bag for the difference.
However, you may have defenses depending on the facts. You may also be able to sue the previous owners or your buyers to request contribution or to indemnify you (or they may sue you, too, on similar theories). So, it is important that you do something about this immediately before the landlord can take a default judgment against you. You should hire a lawyer right away.
-- Thomas Pedreira