A family of Microsoft word processing software products for creating web, email, and print documents.
In Word, can you use File>Share>Email to send a document?
In what format are you trying to send the merged documents? It has been reported in previous versions of Word that sending in another format "unblocks" the one that is not working.
As a work around, download the MergeTools – 20121103 Add-in that I created from the following page of my Windows Live SkyDrive:
and also the Merging with Attachments document that is also on that page which explains how the system is used. It is not actually necessary to have separate attachments as the facility can be used to send just the documents created by the merge itself as attachements, either in the form of Word files or .pdf files.