sharepoint designer 2007 - can not open ASPX page for editing

We have a old sharepoint site built on WSS 3.0 SP3.

Some of the pages (list pages such as newform.aspx) were customized long back using sharepoint designer 2007. I tried to open this page using sharepoint designer 2007 and doesn't open the page for editing.

While opening sharepoint designer 2007 it displayed message indicating the activation needs to be done again due to changes on the server. There have been no changes made to this server. Are we getting this message because sharepoint designer 2007 or WSS 3.0 is not supported anymore?

Is there any way to edit the newform.aspx from the sharepoint site using notepad or other tools without using sharepoint designer.

Any suggestions.