We have a customer using one of our Linux servers as a web host. We had to
change the user's UID, and subsequently chown his files back to him. After
doing this, the Contribute key no longer worked. If a site with a connection
is selected, Contribute fails with:
"Your role in this website is no longer valid. Please obtain a new connection
key." or

If you click on the actual key in Contribute, the error is:
"Contribute cannot find the website files on the server. Please contact the
website's administrator for assistance."

So, we had to create a new key with Dreamweaver for this customer.

Why would changing the UID (which should be transparent to an application)
make any difference? The application itself should not know about the
underlying UID, and the checksum of the file does not change.