Kiosk mode modification - add picture

Hello again,
I'm in the process of trying to import an add-on aircraft into the Kiosk mode of FSX.  All has gone well except for adding a picture to the Kiosk home screen.  I have taken a screen shot, reduced it to the proper dimensions and saved it as a .bmp file using Paint.net, and copied it to the desktop.  The problem arises when trying to add the image to the appropriate .flt file. 
In the past I've used Notepad to enter and similarly modify FS9's [Main] file with no problem.  But with FSX, although I'm able to write the screenshot file into FSX's [Main] file, when trying to close out of Notepad I get the dialog box "C:\Program Files\ etc... \You do not have permission to open this file. See the owner of the file or an administrator to obtain permission." 
I am the only administrator of this computer.  
Any assistance you can offer would be gratefully accepted.  Right now I'm stymied.  Thanks.