When attempting to edit any of the fragments in the Custom Communications sample, Content Creator displays "The content in this resource cannot be edited". I've logged in as the administrator so I don't think it's a rights issue.
There are 2 primary reasons why Content Creator would show this message:
You didn't import the collateral (all the fragments and letter templates) using the CGRImport tool. This tool does 2 things: (a) it sets attributes on the imported assets that lets Content Creator recognize them as various types (since everything is an XDP, Content Creator looks for these attributes to differentiate one XDP from one -- such as an XDP that contains a textual paragraph fragment as opposed to one that contains a regular form with fillable fields), and (b) it sets tags on assets if some were specified during import; OR
The XDP you are trying to view contains something that is causing Content Creator to think it can't edit the content. Textual paragraph fragments are strictly fragments with a single text object in them. Image fragments are strictly fragments witha single image object in them (note that you can only view image fragments at this time).