Thousands of Gilpin County voters received the wrong instructions about how to vote in next month’s election. They were told to enclose a copy of an identification card with their mail-in ballots for their vote to be valid. But Dwight Shellman with the Colorado Secretary of State's Office said that’s wrong.

"That was actually in error,” he said. "The law requires certain voters to enclose a photocopy of an acceptable form of identification when they return that ballot."

Shellman helps county clerks conduct elections. 9NEWS tried calling Gilpin County Clerk Colleen Stewart to see how this happened but she only emailed back a copy of a press release.

The ID instructions Stewart’s office sent out to Gilpin County’s nearly 4,400 registered voters stated that voters needed to make a photocopy of their ID, place it in the mail ballot - or the vote wouldn’t count.

But Shellman said that only applies to newly registered voters. In Gilpin County, only eight people should have received the ID instruction, not all 4,400 registered voters.

So how did this happen?

"I don't really know," Shellman said. "I think it was a simple oversight."

Shellman said once his department heard about the issue, they contacted the Gilpin County's ballot vendor. The vendor confirmed they were told to enclose the ID instruction with all mail ballot packets.

"It's an unfortunate error," he said. "I know it wasn't intentional and it's a reminder that elections are human enterprises and human beings are fallible."

The state is in contact with the Gilpin County clerk. They're sending out postcards to all registered voters addressing the confusion and reminding them - if they plan to vote by mail, they do not need to include a copy of their ID for their vote to count. Again, the ID rule only applies to some new voters.

"It does create confusion," Shellman said. "It's an unfortunate error. It is not a show stopper. I think this is the kind of thing that will resolve itself and it's the kind of thing that happens and we fix it and we move on."

As a reminder, when voters head to the actual polls, they must always show their ID.

Below, you can see the press release sent to 9NEWS by the Gilpin County clerk. Can't see it? Check this link.