Changed error code message to also cover missing pre-shared key
diff --git a/library/error.c b/library/error.c
index 66f0784..7f13067 100644
--- a/library/error.c
+++ b/library/error.c
@@ -274,7 +274,7 @@
         if( use_ret == -(POLARSSL_ERR_SSL_CERTIFICATE_REQUIRED) )
             snprintf( buf, buflen, "SSL - The own certificate is not set, but needed by the server" );
         if( use_ret == -(POLARSSL_ERR_SSL_PRIVATE_KEY_REQUIRED) )
-            snprintf( buf, buflen, "SSL - The own private key is not set, but needed" );
+            snprintf( buf, buflen, "SSL - The own private key or pre-shared key is not set, but needed" );
         if( use_ret == -(POLARSSL_ERR_SSL_CA_CHAIN_REQUIRED) )
             snprintf( buf, buflen, "SSL - No CA Chain is set, but required to operate" );
         if( use_ret == -(POLARSSL_ERR_SSL_UNEXPECTED_MESSAGE) )