Problem with 'Download Link'

Hello all.  I am here today with a mind-boggling problem.  I have built a pretty nice excel download page, which is working great for me.  AND well over 90% of my users.  But there are a select few, to which the link fails.  Basically, I have a 'button' link:

<input type="button" name="Download" value="#strPOName# BLD Draft"
                    onClick="window.open('reports/download_PO_BLDform_Draft.cfm?intPO=#intUserPO#', 'download'); return false;">

For some users, they get the following error message: "Internet Explorer cannot download ...download_PO_BLDform_Draft.cfm from myWebsite".  So, its like it is trying to download the cfm page instead of the excel file being created by the page.  I dont understand why this happens to some people, but I wonder if it has something to do with their particular IE installs, some other software blocking the download?  Has anyone seen this before?

It took me a long time to narrow it down to the code above.  For one user, I worked it down to this, and in another part of the application provided this alternative:

<a href="case/download.cfm?intLaborType=#form.intLaborType#" class="linkButton" target="_blank">Download</a>

For some reason, this link works for them, while the 'button' link does not.  Please help me understand why some people get this error message.  Thanks in advance!