Lisa Artison resigned her post as executive director of the Milwaukee Election Commission, effectively immediately, after being out sick for the past month.

A Milwaukee Journal Sentinel review of city voting records found more than 1,200 people voted from invalid addresses and election officials could not process 1,305 same-day registration cards. Also, 20,000 registration cards were not entered into the system in time, forcing an election-eve scramble to organize them and get them to the polls.

The city also is investigating the problems.

Barrett thanked Artison in a brief statement: "I am most appreciative of Lisa's service during a most difficult election cycle and wish her the best."

Barrett chief of staff Patrick Curley said a management team will continue to oversee the office, which is preparing for the April 5 election. Curley declined to comment on what prompted Artison's resignation.

Artison did not immediately return a message Tuesday from The Associated Press.