The system can not validate an Employer ID number on a W2 and K1. I know that the employers ID number is correct, how do I fix the diagnostic?

[alexlevincpa1]

Prior to 2021 the entity was a single member LLC (reporting as a Sch C) which elected to be treated as an S-Corp, and continued using the same EIN.

[qbteachmt]

From the IRS:

Sole Proprietors

You will be required to obtain a new EIN if any of the following statements are true.

• You are subject to a bankruptcy proceeding.
• You incorporate.
• You take in partners and operate as a partnership.
• You purchase or inherit an existing business that you operate as a sole proprietorship.

[PhoebeRoberts]

From that same page:

You will not be required to obtain a new EIN if any of the following statements are true.

• An LLC that already has an EIN chooses to be taxed as a corporation or as an S corporation.

[George4Tacks]

Call IRS Entity Control 

https://www.irs.gov/businesses/telephone-assistance-contacts-for-business-customers