This copy of Microsoft Office Excel cannot be used on Terminal Server

Good Day to all,
Here is my problem, I have 2 computers. One with Windows 7 and the other with Windows 2003 server installed.
I have office 2007 installed on both the machines. Whenever I try to connect to my terminal server for any excel sheets I get the following error message.
Now how do I convert my retail license to volume license? Any ideas?

Microsoft Office Excel
This copy of Microsoft Office Excel cannot be used on Terminal Server. Please contact your local authorized Microsoft retailer for more information.
