I think that's the error message that's displayed when you haven't entered anything in for the gram weights. Click Tools/Grams Set and put in how many grams = 1ml of nic, PG, VG, water/PGA, and Flavoring. I use 50/50 nic base, so I have for values:
Nicotine: 1.1425
PG: 1.036
VG: 1.249
Water/PGA: 1
Flavoring: 1
Flavoring will vary, depending on what it is (and most flavoring is in a PG base), but I figure "1" is close enough.
The value I have in for my 50/50 nic is a tiny bit off because it doesn't account for the weight of the nicotine powder that's mixed in with the PG/VG, but again, I figure using formula of (PG+VG)/2 is close enough.
One ml of water weighs 1 gram. One ml of PGA weighs 0.789 grams. So, you'll have to enter in value for whichever one you're most likely to use.
Recipes that come pre-installed with ejuice me up were entered into the program before the gram weights feature was added. So, unless you edit them, they work as-is. If you edit them, though, then the gram weight is required in order to avoid that error message.