Elena Nunez of the watchdog group Colorado Common Cause said some voters on Tuesday were being asked for photo identification papers, which is not required under Colorado law. Voters can still use utility bills, bank statements and naturalization documents as valid forms of identification during elections.
Poll workers were ordered to stop demanding photo identification.
Nunez said a number of voters have been given provisional ballots while problems are being resolved.
In Arapahoe County, voters faced long lines with wait times of up to two hours. Long lines were also reported in Denver, Jefferson and other large metropolitan counties.
Election officials did not return phone calls for comment.
(Copyright 2012 by The Associated Press. All Rights Reserved.)