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If Windows Event Viewer shows a SCEP enrollment error with HTTP 429 Too Many Requests and HRESULT 0x801901ad, the message means the enrollment request received a rate-limit response. It does not, by itself, show that your TPM is broken or that Windows needs a repair. Check the full event details before taking action: “Event ID 87” identifies the event, while the HTTP status and HRESULT describe the reported failure.
What does SCEP Event ID 87 mean?
SCEP is a certificate-enrollment protocol. In the Windows reports discussed here, Event ID 87 records an enrollment attempt involving a Microsoft AIK endpoint. The event ID alone is not enough to diagnose the problem: different reports with Event ID 87 contain different HTTP responses and messages.
In a Microsoft Q&A post dated July 15, 2026, a Windows 11 user reported an attempt to contact microsoftaik.azure.net that received HTTP 429, HRESULT 0x801901ad, and a Retry-After: 20 header. The user also reported that the TPM was ready. Those details describe that request; they do not establish why the service rate-limited it or prove a device-wide TPM fault. Read the reported event and discussion on Microsoft Q&A.
How to read the full event message
Open the event in Event Viewer and read its General details. Record the endpoint, HTTP status, HRESULT, response text, and any retry information. These values distinguish a rate-limit response from other SCEP errors; the event ID by itself does not.
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- HTTP 429: the server response says the request was made too often. If that exact event includes
Retry-After, it states a retry interval for that response only. - HRESULT 0x801901ad: the HRESULT recorded with the 429 in the July 15 report. Do not treat it as interchangeable with Event ID 87.
- Endpoint: the reported 429 involved
microsoftaik.azure.net. Confirm the endpoint in your own event rather than assuming every Event ID 87 targets the same service.
How a reported 429 differs from a reported 400
Another Microsoft Q&A report dated July 26, 2026 describes Event ID 87 with HTTP 400 and a response stating that V2 AIK requests with P-256 ECC keys are unsupported. That is a different response from HTTP 429; advice for one should not be applied automatically to the other. Compare the full event details:
| Reported response | Recorded details | What it indicates |
|---|---|---|
| HTTP 429 | HRESULT 0x801901ad; Retry-After: 20 in the July 15, 2026 report; endpoint reported as microsoftaik.azure.net. |
A rate-limit response for that enrollment request. The retry interval is specific to that response. |
| HTTP 400 | The July 26, 2026 report says V2 AIK requests with P-256 ECC keys are unsupported; no comparable retry interval is stated in that report. | A distinct error response that needs diagnosis based on its own message. |
See the separate HTTP 400 report on Microsoft Q&A.
What should you do about repeated 429 events?
- Confirm the response. In Event Viewer, open the SCEP event and verify that it actually contains HTTP 429. Note its HRESULT, endpoint, and any
Retry-Aftervalue. - If this is a work- or school-managed PC, contact the administrator. Certificate enrollment can involve organizational configuration or policy, and the available reports do not establish that changing a scheduled task is generally safe or recommended.
- For a personal PC, keep the complete event details and watch whether the entries continue. User reports say some repeated events later stopped, but they do not identify a cause, predict when that will happen, or establish an official fix. See the user discussion on ElevenForum.
- If the event shows HTTP 400 or a different response, troubleshoot that message separately. Do not use the 429 interpretation as a diagnosis for another status.
Does Event ID 87 mean the TPM is faulty or requests are building up?
No such conclusion follows from the event alone. The July 15, 2026 429 report also described the TPM as ready, and the cited discussions do not establish that the message means requests are accumulating in a way that will damage Windows or the device. They also do not confirm a specific Windows update as the cause or establish a universal Microsoft-approved fix.
Do not clear the TPM or replace it solely because of this 429 message. The reports provide no evidence that either action resolves the rate-limit response. If the event is recurring on a managed device, an administrator can assess the enrollment setup; for other cases, use the complete event details rather than the event number alone.
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