(a) General rule. Except as provided in paragraph (b) of this section, benefits accrued under a plan after the date on which the Secretary of the Treasury or his delegate issues a notice that any trust which is part of the plan no longer meets the requirements of section 401(a) of the Code or that the plan no longer meets the requirements of section 404(a) of the Code or after the date of adoption of a plan amendment that causes the issuance of such a notice shall not be guaranteed under this part.

(b) Exceptions. The restriction on the guarantee of benefits set forth in paragraph (a) of this section shall not apply if:

(1) The Secretary of the Treasury or his delegate issues a notice stating that the original notice referred to in paragraph (a) of this section was erroneous;

(2) The Secretary of the Treasury or his delegate finds that, subsequent to the issuance of the notice referred to in paragraph (a) of this section, appropriate action has been taken with respect to the trust or plan to cause it to meet the requirements of sections 401(a) or 404(a)(2) of the Code, respectively, and issues a subsequent notice stating that the trust or plan meets such requirements; or

(3) The plan amendment is revoked retroactively to its original effective date.