I have also experienced this error message and found through trial and error that this could also mean the voucher code you entered is incorrect. I purchases a Public Mobile Top Up voucher from a Loblaws grocery store - the voucher details are issued on the lower portion of the printed receipt. There are two 12 digit numbers found in the details - one is called "VOUCHER #" and the other "PIN#". On the Public Mobile site, after logging in, if you select: Payments - Redeem Payment Voucher, the site prompts for the Payment Voucher Code. - if you enter the PIN# in this field, the site will accept the voucher and show the top-up value you purchased. If you enter the VOUCHER# from the receipt the site accepts it but it will say it cannot process the number at this time and to try again later (but it will never process this number so remember to use the PIN#)
