invalid server's version String

[Sundaram]

while connecting from one particular server, I am getting this error. While in other server it's running fine.

Following code causes problem:
if(i==buf.buffer.Length ||
i<7 ||                                      // SSH-1.99 or SSH-2.0
(buf.buffer=='1' && buf.buffer!='9')  // SSH-1.5
)
{
                        throw new JSchException("invalid server's version String ") ;
}

The below condition becomes true:
i==buf.buffer.Length

Any idea why it's failing on one particular server?