TeamViewer is not connecting to Master Server, how can i do?

I am using Teamviewer for desktop sharing. I have a LAN of 20 computers connected to Internet. I try to log in through teamviewer to access one of my client’s desktop but an error of Master Server is preventing me to do so.
I am using windows XP SP2. The error message is as follows; Please check your internet connection. Most likely you use a proxy server and you have to enter the proper information in the options dialog.“Retry” will be returned in 25 seconds.

I have performed the Retry operation several times but not fruitful result.
I hope someone help me about this issue.
