InfoPath Dev

I've been working on this form the last couple of days. I recently made a change to the 'header' through page setup. When I tried to open the form in design mode I get the following error:

The form definition (.xsf) file contains elements, attributes, or structures that are not valid.

Error details:
Element 'http://schemas.microsoft.com/office/infopath/2003/solutionDefinition}header' is unexpected according to content model of parent element 'http://schemas.microsoft.com/office/infopath/2003/solutionDefinition}printSettings'.

Line 188, Position 17
<xsf:header>
----------------^

How do I get the .xsn open so that I can get to the .xsf?

The .xsn file is just a .cab file. You can rename it to .cab and then extract the source files out. Then you can open the manifest.xsf file in notepad, and remove the xsf:header block. When done, right-click the manifest.xsf file and choose design. Then save your template back to a .xsn file.