Universal Cryptoki function return values

Any Cryptoki function can return any of the following values:

CKR_GENERAL_ERROR: Some horrible, unrecoverable error has occurred. In the worst case, it is possible that the function only partially succeeded, and that the computer and/or token is in an inconsistent state.
CKR_HOST_MEMORY: The computer that the Cryptoki library is running on has insufficient memory to perform the requested function.
CKR_FUNCTION_FAILED: The requested function could not be performed, but detailed information about why not is not available in this error return. If the failed function uses a session, it is possible that the CK_SESSION_INFO structure that can be obtained by calling C_GetSessionInfo will hold useful information about what happened in its ulDeviceError field. In any event, although the function call failed, the situation is not necessarily totally hopeless, as it is likely to be when CKR_GENERAL_ERROR is returned. Depending on what the root cause of the error actually was, it is possible that an attempt to make the exact same function call again would succeed.
CKR_OK: The function executed successfully. Technically, CKR_OK is not quite a "universal" return value; in particular, the legacy functions C_GetFunctionStatus and C_CancelFunction (see Section 11.16) cannot return CKR_OK.

The relative priorities of these errors are in the order listed above, e.g., if either of CKR_GENERAL_ERROR or CKR_HOST_MEMORY would be an appropriate error return, then CKR_GENERAL_ERROR should be returned.

RSA Security Inc. Public-Key Cryptography Standards - PKCS#11 - v210