That code represents a duplicate filing... Have you (or someone else) already filed a return with your SSN on it? Double check the entries on your tax return.
If you've double-checked that the information is correct, it's likely that somebody filed a fraudulent return using your information. If that is the case, follow the information in these links to protect yourself against identity theft:
You won't be able to e-file because your Social Security number or ITIN has already been accepted. Instead, you'll need to print and file your return.
How do I fix reject code IND-452?
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