Issue using deviceidmanager for an Azure WebJob command line

I have build a command line app which connects to CRM and outputs some data to an FTP location.  It is working well.

I thought I would deploy it to Azure as a WebJob so that it could be scheduled.

I received errors from the deviceidmanager relating to the file location of the deviceid details.  I found an article and made the changes below which seemed to fix the issue.

private static class LiveIdConstants
        {
            public const string RegistrationEndpointUriFormat = @"https://{0}/ppsecure/DeviceAddCredential.srf";

            public static readonly string FileNameFormat = Path.Combine(
                Environment.GetEnvironmentVariable("WEBROOT_PATH"),"{0}{1}.xml");

            public const string ValidDeviceNameCharacters = "0123456789abcdefghijklmnopqrstuvqxyz";

            //Consists of the list of characters specified in the documentation
            public const string ValidDevicePasswordCharacters = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789!@#$%^*()-_=+;,./?`~";
        }


private string Encrypt(string value)
        {
            if (string.IsNullOrEmpty(value))
            {
                return value;
            }

            byte[] encryptedBytes = ProtectedData.Protect(Encoding.UTF8.GetBytes(value), null, DataProtectionScope.LocalMachine);
            return Convert.ToBase64String(encryptedBytes);
        }

        private string Decrypt(string value)
        {
            if (string.IsNullOrEmpty(value))
            {
                return value;
            }

            byte[] decryptedBytes = ProtectedData.Unprotect(Convert.FromBase64String(value), null, DataProtectionScope.LocalMachine);
            if (null == decryptedBytes || 0 == decryptedBytes.Length)
            {
                return null;
            }

            return Encoding.UTF8.GetString(decryptedBytes, 0, decryptedBytes.Length);
        }

Note the use of LocalMachine the WebRoot Path.

Things were fine for 24 hours and then I started getting the following error:

System.InvalidOperationException: Unable to Deserialize XML (Operation = Loading Device Credentials from Disk):

System.InvalidOperationException: There is an error in XML document (5, 5). ---> System.Security.Cryptography.CryptographicException: Key not valid for use in specified state.

at System.Security.Cryptography.ProtectedData.Unprotect(Byte[] encryptedData, Byte[] optionalEntropy, DataProtectionScope scope)

[09/02/2016 14:38:00 > 86fffa: INFO]    at Microsoft.Crm.Services.Utility.DeviceUserName.Decrypt(String value) in C:\Projects-Online\***\LetterBatchTool\Helpers\deviceidmanager.cs:line 981

I am unsure why the code worked and then broke without intervention.  It had been running every hour for testing purposes. 

Could the file have become corrupt?  Do I need the file? Is there maybe a way to bypass it or store the data another way?  Perhaps a simple amendment to make it use hardcoded values or create the data fresh every time?