when you filed that 2553 did you elect a fiscal year because generally S-elections are made on a calendar year basis. check the response from the IRS as to when the tax year starts.
also fiscal year selection may be invalid if it is not a valid business year
from 2553 instructions
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It has or will adopt or change to one of the following tax years.
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A tax year ending December 31.
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A natural business year.
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An ownership tax year.
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A tax year elected under section 444.
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A 52-53-week tax year ending with reference to a year listed above.
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Any other tax year (including a 52-53-week tax year) for which the corporation (entity) establishes a business purpose.
For details on making a section 444 election or requesting a natural business, ownership, or other business purpose tax year, see the instructions for Part II.
also, the S-corp would have a different EIN then the one the sole proprietorship had (if any). I agree @AmeliesUncle consult a pro.
