A super PAC tied to Paul Manafort tried to explain on Tuesday to the Federal Election Commission why it failed to report a $1 million contribution it received one week before the 2016 election.

Rebuilding America Now PAC sent a letter laying out its position on the “inadvertent omission,” telling the FEC that a series of clerical errors had led to its failure to report the $1 million contribution.

The note also revealed that the PAC conducted an internal audit in late September 2018. That mans the audit came around roughly the same time as Manafort was cooperating with the special counsel’s investigation. A federal judge later found that Manafort lied to prosecutors during those sessions about a mysterious $125,000 payment from a vendor of Rebuilding America Now that supposedly went towards paying down a debt Manafort had to a law firm.

The FEC first demanded an explanation for why the $1 million wasn’t accounted for on the group’s monthly filing that covered the weeks before the 2016 election in a February 2019 letter.

The missing contribution came from Los Angeles real estate magnate Geoffrey Palmer, who gave a total of $6 million to Rebuilding America Now during the 2016 election cycle. The PAC spent a total of $23 million during the same period.

Ryan R. Call, treasurer for the PAC, wrote in the Tuesday letter that Palmer had contributed $1 million 11 days before the omitted donation was made, leading Call to believe that it was a “duplicate entry” and to remove it from the original filing.

When reconciling the committee’s end-of-year books, the PAC discovered that Palmer had made two $1 million contributions in October 2016, but only corrected the overall balance for its year-end report to the FEC, and did not add a reference to the missing million.

It wasn’t until late September 2018, the committee writes, that it discovered during an “internal audit” that information about the $1 million was missing.

It’s not clear what prompted the September audit. Larry Noble, a former FEC general counsel, told TPM that PACs tend not to conduct audits “just for the heck of it. Usually, something triggers it.”

Rebuilding America Now says that it had conducted the audit “in late September of 2018 in advance of the 2018 General Election (during which the Committee was not active in conducting electioneering activities).”

Around this time, court filings show, Paul Manafort was sitting through hours of sessions with FBI agents after his cooperation agreement began on Sept. 14. The cooperation agreement would later fall apart, and prosecutors called off the deal.

This isn’t the first time the PAC has attracted FEC scrutiny.

In June 2018, the FEC sent a letter asking Rebuilding America Now to provide more information on the travel expenses that its executives claimed. Laurance Gay, the PAC’s director who oversaw ticketing for the Trump inaugural committee, took $42,286 from Rebuilding America Now for “travel” in the first three months of 2018.

The PAC does not appear to have replied to that request.