The Senate campaign of Republican Rep. Todd Akin has yet another problem – the candidate has once again run afoul of Congressional financial disclosure rules.

Akin spent 12 years in the Missouri House, service that has earned him about $129,000 in a state employee pension that, for some reason, he neglected to include on his Congressional disclosure forms.

Akin made the acknowledgement in a Tuesday letter to House Ethics Chairman Jo Bonner (R-Ala.), amending a decade’s worth of disclosure forms.

“It has come to my attention that I have inadvertently filed my Financial Disclosure Reports for Calendar Years 2002-2011 without including a pension (not self-directed) from the State of Missouri,” Akin wrote. “This was an unintentional oversight and I regret any inconvenience this may cause.”

A source close to Akin’s office stressed that the staff was not involved in the most recent financial disclosure filings. Akin conceded the error after the St. Louis Post-Dispatch questioned why the pension benefits did not appear on his forms.

This is not the first time Akin has been caught omitting information on a disclosure form. Last year, he filed an amendment to about a decade’s worth of disclosure forms because property holdings that were worth at least $355,000 in 2010 had not been reported.

Akin mistakenly believed that he did not need to list the property holdings because they were in a limited partnership that he did not have financial control over, as Roll Call reported at the time.

According to revised disclosure filing last year, the city of St. Louis appraised the value of two lots – of which Akin is part owner – at about $750,000.

Akin had sought advice from the Ethics Committee about the properties in response to another query from the St. Louis Post Dispatch. It is unclear why it did not occur to Akin or anyone associated with his office to report the undisclosed pension income at that time.

The new financial disclosure issue is just the latest in a series of unforced errors by Akin that have undermined his effort to unseat Sen. Claire McCaskill (D). Those missteps appear to be validating the decision of the National Republican Senatorial Committee to pull out of the race and spend its money in other states in a bid to gain control of the Senate.

Missouri voters seem to want Republicans to take control of the Senate, but polls indicate they’re unwilling to vote for Akin to help accomplish that goal.

McCaskill had a 6-point lead in the two most recent public polls and a 9-point lead in a recent internal poll conducted for her campaign. An internal poll conducted for the Akin campaign reportedly showed the Republican about 4 points ahead.

Roll call rates the Missouri Senate race as Leans Democratic.

Janie Lorber contributed to this story.