It appears, however, that members of the public who used the Mobiles.co.uk website only, had their details submitted once and were sent an automated rejection email if they failed.
Customers of other online retailers including Mobile Phones Direct, Affordable Mobiles and Fonehouse have reported experiencing a similar fate.
"Due to the high volume of interest in our Black Friday deals, the system dealing with credit applications from indirect partners experienced some issues," said a spokeswoman for Vodafone.
"This meant that a small number of applications were declined incorrectly.
"The system is now back up and running properly and we are rechecking applications from anyone who has contacted us to query our decision on their application.
"These customers will still be able to take advantage of our Black Friday offers."
Vodafone added that the follow-up checks would not affect consumers' credit scores.

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Dixons Carphone has acknowledged that some of its customers have still to be told whether or not they have been accepted, but it has not acknowledged Vodafone's accuracy problem.
"Due to an incredibly high take-up of our very competitive Black Friday deals with Vodafone, there is a backlog processing credit checks," said a spokeswoman.
"We're working with Vodafone to resolve this and the backlog is expected to be cleared by the end of the week.
"Vodafone has told us they will honour the deals for those customers who ultimately pass the credit checks."
One industry expert expressed surprise that Dixons Carphone had not addressed the failed credit checks.
"If you're going to offer a promotion that almost looks too good to be true, the likelihood is that you are going to get deluged with people and you have to be able to cope with that as an organisation," said Ben Wood from CCS Insight.
"If something then goes wrong you have to address that