I’ve found that if you create a Web Part Connection between two Web Parts using the SharePoint UI, you cannot reliably remove the connection. After you remove the connection, if you remove one of the connected Web Parts, you often get an error that SharePoint can’t find the identifier of the removed Web Part. This can leave your site in a permanently broken state.
The solution is to remove the connection in SharePoint Designer. Removing it there seems to do the job more completely.
UPDATE 10/1/2007: Just to elaborate a bit (since I ran into this again today), here’s the easy way to do this. If you get the error about the Web Part Connection, it will look like:
Could not find the connection provider Web Part with ID "g_2df2bab0_40ee_4955_9e8b_bfce21bb937f".
Copy that nice looking ID (g_2df2bab0_40ee_4955_9e8b_bfce21bb937f) and open the aspx page in SharePoint Designer. Go into code view and search for the ID. It will live in a code block that looks something like this, in one of the two locations highlighted in red:
<WebPartPages:SPWebPartConnection ID="g_D0184680A5C14C6286A98B8C8236B091" ConsumerConnectionPointID="DFWP Parameter Consumer ID" ConsumerID="g_ac7e15f7_3724_4a37_a059_9de6481a2835" ProviderConnectionPointID="DFWP Row Provider ID" ProviderID="g_2df2bab0_40ee_4955_9e8b_bfce21bb937f"> <asp:rowtoparameterstransformer ProviderFieldNames="@ID" ConsumerFieldNames="listItemID" />
The bolded section is what you want to delete. (If this is the only Web Part Connection on your page, you can also delete the <SPWebPartConnections></SPWebPartConnections> surrounding tags.)