Is the building block in the template you gave to the client or is somewhere on your machine (eg Normal.dotm or Building Blocks.dotx).
In older versions of Word - pre 2010 (and in some older compatibility modes) the Title property wasn't available. So you could ensure that the document is not in Compatibility Mode or more recent that 2007 before working with the table title.
Code:
ActiveDocument.SetCompatibilityMode wdWord2010
Selection.Tables(1).Title = "Hi Mum" 'this works
ActiveDocument.SetCompatibilityMode wdWord2007
Selection.Tables(1).Title = "Hi Mum" 'this throws 445 error
ActiveDocument.SetCompatibilityMode Application.Version 'set version to match Word version