What Service Pack is installed on that machine? I would suggest updating
it. See my previous post before. (I appreciate that you're running 2003
not 2002 but still...)

http://groups-beta.google.com/group/...5b28fa24bcbd2d

ben wrote:
I have a self-cert that is attached to a project made for multiple machines.
On one of the machines (Win XP, Office 2003) will without any alerts at all
discard the signature before saving the document. No VBA code is changed (The
project is locked.) and all that is changed is the spreadsheet data itself.
It will not even say that the signature is invalid and will be discarded, it
simply discards it without warning, and we only now when we re-open the doc.
Any Ideas as to why this might happen?
Ben