have "Works"? If so is it the same version?
Assuming the database actually contains data, (rather than just being an empty template), it could be quite large file. That in itself can sometimes stop the attachment beig receiving because of isp file size limits.
Are they actually receiving the database OK?
I fthet are getting it, they should probably try saving it from the email and then opening it, rather than trying to open the attachment.
Can you open it ok, saving saved and closed it?
Other than that I have no ideas.