var CADESCOM_CADES_X_LONG_TYPE_1 = 0x5d;
        var CAPICOM_CURRENT_USER_STORE = 2;
        var CAPICOM_MY_STORE = "My";
        var CAPICOM_STORE_OPEN_MAXIMUM_ALLOWED = 2;
        var CAPICOM_CERTIFICATE_FIND_SUBJECT_NAME = 1;

        function GetErrorMessage(e) {
            var err = e.message;
            if (!err) {
                err = e;
            } else if (e.number) {
                err += " (" + e.number + ")";
            }
            return err;
        }

        function CreateObject(name) {
            switch (navigator.appName) {
                case "Microsoft Internet Explorer":
                    return new ActiveXObject(name);
                default:
                    var cadesobject = document.getElementById("cadesplugin");
                    return cadesobject.CreateObject(name);
            }
        }

        function GetVal() {
            var str = '';
            var elems = document.getElementById('signData').getElementsByTagName('INPUT');
            for (var i = 0; i < elems.length; i++) {
                str += elems[i].value;
            }
            alert(str);
        }

        function SignCreate(certSubjectName, dataToSign) {
            var oStore = CreateObject("CAPICOM.Store");
            oStore.Open(CAPICOM_CURRENT_USER_STORE, CAPICOM_MY_STORE, CAPICOM_STORE_OPEN_MAXIMUM_ALLOWED);
            var oCertificates = oStore.Certificates.Select();
            if (oCertificates.Count == 0) {
                alert("Certificate not found");
                return;
            }
            var oCertificate = oCertificates.Item(1);
            var oSigner = CreateObject("CAdESCOM.CPSigner");
            oSigner.Certificate = oCertificate;
            oSigner.TSAAddress = "http://cryptopro.ru/tsp/";

            var oSignedData = CreateObject("CAdESCOM.CadesSignedData");
            oSignedData.Content = dataToSign;

            try {
                var sSignedMessage = oSignedData.SignCades(oSigner, CADESCOM_CADES_X_LONG_TYPE_1);
            } catch (err) {
                alert("Failed to create signature. Error: " + GetErrorMessage(err));
                return;
            }

            oStore.Close();

            return sSignedMessage;
        }

        function Verify(sSignedMessage) {
            var oSignedData = CreateObject("CAdESCOM.CadesSignedData");
            try {
                oSignedData.VerifyCades(sSignedMessage, CADESCOM_CADES_X_LONG_TYPE_1);
            } catch (err) {
                alert("Failed to verify signature. Error: " + GetErrorMessage(err));
                return false;
            }
            return true;
        }

        function run() {
            var signedMessage = SignCreate("erwer", GetVal());
            var verifyResult = Verify(signedMessage);
            if (verifyResult) {
                document.data.signedForm.value = signedMessage;
                //alert("Signature verified");
            }
        }

        function isPluginInstalled() {
            switch (navigator.appName) {
                case 'Microsoft Internet Explorer':
                    try {
                        var obj = new ActiveXObject("CAdESCOM.CPSigner");
                        return true;
                    }
                    catch (err) { }
                    break;
                default:
                    var mimetype = navigator.mimeTypes["application/x-cades"];
                    if (mimetype) {
                        var plugin = mimetype.enabledPlugin;
                        if (plugin) {
                            return true;
                        }
                    }
            }
            return false;
        }

byte[] encodedSignedCms = System.Text.Encoding.Default.GetBytes(Request.Params["SignedForm"]);

byte[] srcData = System.Text.Encoding.Default.GetBytes(Request.Params["user"]+Request.Params["name"]);

ContentInfo contentInfo = new ContentInfo(srcData);

SignedCms signedCms = new SignedCms(contentInfo, true);
signedCms.Decode(encodedSignedCms);
тут ошибка