Source: Windows can't fax or preview the attached file type - Problems with Windows FAX - Overclockers Forums
The fie type you are trying to Fax no longer has the printto command associated with it.
I used this freeware: Types
Let's say you can't fax a .jpg file.
1. Open the freeware program and type inside it jpg
This will automatically scroll down the list of extensions to jpg.
2. Double click on jpg to open its options.
3. Actions TAB
4. Next to green + type in
5. Click on green +
6. Select newly added printto
7. Next to yellow folder icon paste this
rundll32.exe C:\WINDOWS\system32\shimgvw.dll,ImageView_PrintTo /pt "%1" "%2" "%3" "%4"
Repeat for all file types you are having problems faxing.
.bmp .gif .giff .jpe .jpeg .jpg .pbm .png .tif .tiff
.pdf .doc .xls