Actually, a new EIN is not required when an LLC taxed as a partnership elects Subchapter S status.  It’s confusing on the IRS website, but I checked with them when the election was made and was told their EIN would not change.  
The problem is in the Proseries Professional software that recognizes the tax ID from the previous year’s 1065, since there isn’t a way to convert from 1065 to 1120S.