Same thing happened to me and I did email Disney and got an email back a few days later. Bottom line, on the passholder page the way it's set up to enter the number on the back of the voucher is confusing. My type of vouvher was the last choice and the info we nt something like NBV# then the date then 3 letters:three numbers and then... my voucher had 8 more numbers (#### ####). It looked to me as tho the directions were saying I could enter 5 numbers (#...####) or something like that - just omit the first 3 of that grouping but it NEVER worked. Finally, the email I got back from Disney instructed me to enter only the last 4 numbers (not 5). It worked! So if your last 8 numbers are 1234 5678, try just entering the 5678 in that last section.
GOOD LUCK!
ps - I sent Disney another email to say that their instructions are CONFUSING!