I am having the same issue--two of my children's federal returns were rejected for the 8615 Line 7 error. Finding no answers on Turbotax site, I paid the extra money to get the Turbotax Live (live tax person supposed to help). The live person remoted into my computer and concluded that it was a Turbotax computation glitch and advised that I return on March 19 b/c the glitch will be fixed. So, I had to pay extra money to Turbotax to be told the error was on their end...SMH. Better yet, when I returned to fix the tax return today (March 20), the software clearly has not been fixed b/c it is coming up with the same amount for the return--the amount that the Feds rejected.
