Okay, I have a general fix for this. Replace the fuel section - EACH TIME YOU LOAD THE 707-300B/ADV/C or VC-137 - with the following:

[fuel]
fuel_type=2
number_of_tank_selectors=4

Center1=  0,   0, -2, 10300, 0
Center2= -2, -15,  0, 4129, 0
Center3= -2,  15,  0, 4129, 0
LeftMain=-16, -37,  3, 2357, 0
RightMain=-16,  37,  3, 2357, 0
LeftAux=-29, -58,  5, 454, 0
RightAux=-29,  58,  5, 454, 0

This may have already been posted, but it is a good fix. Once you replace it (whenever you plan to use aircraft I listed above and after using TCE to configure these particular aircraft), you can load the required fuel onboard using FS Fuel and Payload loader. Just remember not to attempt to edit payload from this menu - or FS will experience CTD. 

Hopefully this will be fixed with the next version.