Linda Cardenas wanted her dad's mail-in ballot to count, so she personally delivered the ballot to the post office.

The U.S. Postal Service, though, returned the ballot to her dad.

Undeterred by the apparent mistake, Cardenas mailed the ballot again — and the ballot was returned a second time.

Frustrated, she called the Hidalgo County Elections Department.

Elections Administrator Yvonne Ramon said a handful of voters experienced similar problems with the Postal Service.

"We've had approximately six voters call saying that they received their mail ballot back in their home. So what we did is we called the post office and we asked what is happening," Ramon said. "And apparently — we've always used this envelope, we've always used the same format, but, lo and behold, this year the scanner was reading the back side of the carrier envelope instead of the front side."

The Elections Department contacted the Texas Secretary of State's Office, which informed Ramon that Dallas County had experienced the same problem.

Anyone who experiences problems with a mail-in ballot should drop off the ballot by hand at the Elections Department.

For details on how to drop off a ballot, call the Elections Department at (956) 318-2750.

Watch the video for the full story.