A business return may be rejected with code R0000-900-01:
The return type indicated in the return header must match the return type associated with the IRS for the EIN.
The reasons for this reject can vary depending on the entity type, but the resolution process is the same for all:
Mail the return.
Contact the IRS E-help Desk for guidance on the next steps. For more information about the E-help Desk, see here.
S Corporation
For an S corporation return, there are several potential reasons for this reject:
If the reject occurs in a year other than the C corporation’s first year, it may indicate that the C corporation did not file Form 2553 to elect S corporation status. As a result, the IRS still recognizes it as a C corporation and expects a Form 1120 filing. (Note: Form 2553 is filed separately from the tax return, by mail or fax, and not included with the return.)
The corporation may have received Notice CP261 from the IRS approving the S corporation election, but with an effective date for the next year, not the current year.
The state where the entity is incorporated has informed the IRS that the business is no longer in good standing, effectively dissolving the corporation in both state and IRS records. (You can generally confirm this by checking the state's Secretary of State business search website.)
The IRS records may reflect the business as a different entity type, such as a partnership filing Form 1065, a C corporation filing Form 1120, or a disregarded entity reporting on Schedule C with the owner’s individual return.
Partnership
For a partnership return, this reject typically indicates that a different type of return was filed for the EIN in the prior year. This suggests that the business was not a partnership last year, and it should have applied for a new EIN when the partnership was formed.