If you have a "B" visa stamped in your passport you do not need to complete the ESTA form on-line. The "B" Visa is a visa. The ESTA form is for those people that do not have a visa. You have a visa. Because you have a visa, you do not need to follow the process for those people that do not have a visa.
Much of the above may be found on the internet, by googling ESTA - just a thought