Error message “Word Can Not Open this Document Template (C:.\…\14\Built-In-Building Blocks.dotx)” appears when trying to add page numbers or doing other operations related to headers and footers.

This is often caused by corrupted Building Blocks.dotx file.

• Close Microsoft Office
• Navigate to: “C:\Users\<user.name>\AppData\Roaming\Microsoft\Document Building Blocks\1033\14” and delete two files:
  Building Blocks.dotx
  Built-In Building Blocks.dotx
• These files will be re-created by MS Word automatically.

Windows 7
MS Word 2010