Key not valid for use in specified state

[hope4555]

Hello
Was working for us for a long while
After the last windows update we get this:

could not create pfx file: System.Security.Cryptography.CryptographicException: Key not valid for use in specified state.

at System.Security.Cryptography.Utils.CreateProvHandle(CspParameters parameters, Boolean randomKeyContainer)
at System.Security.Cryptography.Utils.GetKeyPairHelper(CspAlgorithmType keyType, CspParameters parameters, Boolean randomKeyContainer, Int32 dwKeySize, SafeProvHandle& safeProvHandle, SafeKeyHandle& safeKeyHandle)
at System.Security.Cryptography.RSACryptoServiceProvider.GetKeyPair()
at System.Security.Cryptography.RSACryptoServiceProvider..ctor(Int32 dwKeySize, CspParameters parameters, Boolean useDefaultKeySize)
at System.Security.Cryptography.RSACryptoServiceProvider..ctor(CspParameters parameters)
at Oocx.Asn1PKCS.PKCS12.Pkcs12.CreatePfxFile(RSAParameters key, String pathToCertificate, String password, String pathToPfx) in C:\projects\acme-net\src\Oocx.Asn1PKCS\PKCS12\Pkcs12.cs:line 16
at Oocx.ACME.Console.AcmeProcess.SaveCertificateWithPrivateKey(String domain, RSAParameters key, String certificatePath) in C:\projects\acme-net\src\Oocx.ACME.Console\AcmeProcess.cs:line 93

Ideas?