Error when try to edit a page in SharePoint Designer

[micarreiro]

When I try to edit a page in Microsoft Office SharePoint Designer 2007, I receive the message "This page cannot be edit in SharePoint Designer (...)".

So, I Detach the page from Page Layout but, after accept the first message to continue, I receive another message: "Object reference not set to a instance of a object", and the page cant be edited. It doesnt occur in all pages.

What can I do?



Tks