base 64 encoding

I am trying to convert base 10 value to base 64 but load runner is converting it incorrectly. 

base 10 value= 463076212249 
Expected base 64 value = GvRfj4Z 
Load Runner Output= NDYzMDk0MDAzNjU5 

#include "mic_socket.h" 
Action() 
{ 
char *encodedMessage; 
lr_load_dll("micsocket.dll"); 

encodedMessage = util_base64encode("463076212249"); 

lr_message( "The encoded message is: '%s' ",encodedMessage ); 
return 0; 
} 

you can check the correct value on website: http://convertxy.com/index.php/numberbases/ 

Please suggest how to get the correct value in VUGen.