Check your data: When I copy and paste your code and data:
private void butTestIt_Click(object sender, EventArgs e)
{
string str = "rb3Cmy54Q8sANMHkelt9QzqOnM3enifu6v7AG5567oiqDk5ijwSwcSzfxUgHm4xD";
MemoryStream ms = Demo(str);
}
public static MemoryStream Demo(string str)
{
MemoryStream memoryStream = new MemoryStream(Convert.FromBase64String(str));
return memoryStream;
}
I get no error at all: the buffer is fine, and 48 bytes long.