Keyset does not exist /r /n - sharepoint-2010

Question

I was tasked to create a integration service between our SharePoint app and one service provider. One requirement of the service provider I'm going to integrate with is to provide them a public key which they will use to verify my request which was signed using our own private key.
Initially I created a console app which reads the certificate store and gets the private key which to use to sign my request and all. The console app works fine so I decided to move it now within our SharePoint application. Unfortunately it fails in this specific part of the code:
key.FromXmlString(privateCert.PrivateKey.ToXmlString(true));
The whole code snippet which gets the certificate and does the signing can be found below:
X509Certificate2 privateCert = null;
X509Store store = new X509Store(StoreName.My, StoreLocation.LocalMachine);
store.Open(OpenFlags.MaxAllowed);
var certs = store.Certificates.Find(X509FindType.FindByThumbprint, "thumbprinthere", true);
if (certs.Count > 0)
{
privateCert = certs[0];
}
RSACryptoServiceProvider key = new RSACryptoServiceProvider();
key.FromXmlString(privateCert.PrivateKey.ToXmlString(true));
byte[] sig = key.SignData(Encoding.ASCII.GetBytes(data), CryptoConfig.MapNameToOID("SHA256"));
string signature = Convert.ToBase64String(sig);
[UPDATE]
I tried following the steps in this link. I first uninstalled my existing private key in the server. I then imported it back to the Certificate store and confirmed that there was a Thumbprint property. After that, I ran findprivatekey.exe and was able to navigate to the MachineKeys folder. From there I added different users ranging from Network Services, IIS_IUSRS and even local accounts I used to login to the server as well as SPFarm admin but I still keep getting the error.
I also made sure that the key I added was exportable so there should be a way for it the application to extract the private key attached to the certificate.
[UPDATE 2]
I updated the code so that it just returns one certificate prior to assigning it to the variable I was using to extract the private key. Still the same issue even if I can see that the certs variable is returning exactly one record.

Answer 1

After much checking I realized I missed one important part in calling the method code block above. I forgot to wrap it an elevate privilege block. After doing that, the code functioned similarly as my console app.
SPSecurity.RunWithElevatedPrivileges(delegate())
{
...
X509Certificate2 privateCert = null;
X509Store store = new X509Store(StoreName.My, StoreLocation.LocalMachine);
store.Open(OpenFlags.MaxAllowed);
var certs = store.Certificates.Find(X509FindType.FindByThumbprint, "<thumbprinthere>", true);
if (certs.Count > 0)
{
privateCert = certs[0];
}
RSACryptoServiceProvider key = new RSACryptoServiceProvider();
key.FromXmlString(privateCert.PrivateKey.ToXmlString(true));
byte[] sig = key.SignData(Encoding.ASCII.GetBytes(data), CryptoConfig.MapNameToOID("SHA256"));
string signature = Convert.ToBase64String(sig);
...
});