Cannot open Infopath attachments in Outlook 2007

I have built an InfoPath form and web enabled it. Users fill in the form in Internet Explorer and attach a file to it. When they press the “Save” button, a mail is sent to some receivers in Outlook. When they try to open the form, they get the following error:

Enlarged error:
I will try to translate the above error message here: “Infopath cannot open the following file c:documents….” “The file is not a valid xml file”. “The form contains XML that cannot be parsed”. An invalid character was found in the content” and then it complains on the formatting of my attachment field which in this case is “fält2”.
After I press OK on the error message the form opens up as a normal mail, and not in InfoPath as expected:
As you can see, the mail attachment has been converted to an empty textbox!
The attachment is removed, because if I try to open the attached form.xml file I get the same error in InfoPath.
This happens to ALL types of files, except .txt files. If the user attach a .txt file and the form is opened in Outlook, it opens correctly and you can see that attached file:
I have this case at Microsoft right now, and will tell you the solution to this as soon as I get it.