Excel 2007 - changing connection properties

[Ben]

Hi all,

We have a spreadsheet that was set up to link to a database via a
system DSN. To simplify deployment of this, I'd like to change this
to connect via the connection string below:

DRIVER=SQL Server;SERVER=xxx;UID=xxx;PWD=xxx;DATABASE=xxx;

I've done this for another spreadsheet, and it was easy (Data tab-

Connections->Properties), but in this next spreadsheet the Connection

Properties for one connection are greyed out/disabled, so I can't
change the string.

Does anyone have any ideas how to enable these values again so I can
change the connection string?

thanks!
Ben