HRESULT 0x80100009 (SCARD_E_UNKNOWN_READER): meaning and diagnosis

Status / error code:

Category:

Constant name:

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Operating System:

Description:

The specified reader name is not recognized.

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SCARD_E_INSUFFICIENT_BUFFER	SCARD_E_TIMEOUT

SCARD_E_UNKNOWN_READER

SCARD_E_UNKNOWN_READER The reader name supplied by the caller is not recognized. Reader names are assigned by the PC/SC subsystem and can change after reinstalling drivers, reconnecting USB devices, or switching remote sessions.

What to check

Enumerate current reader names with SCardListReaders instead of storing a name permanently in application configuration.
Check the correct Windows session and device path, especially when using Remote Desktop smart-card redirection.
If the physical reader is missing from the list, troubleshoot driver or service detection before attempting card operations.

Microsoft: SCardListReaders

Microsoft: Smart Card Plug and Play

Microsoft: Smart Card Minidrivers

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