Arnold is Probably Thinking That This Is One of Those Situations Where a Cyborg from the Future Would Have Come in Handy

It just doesn’t seem possible that his Govinatorness would have a tax lien slapped on him because A) he’s married to a Kennedy and B) his annual Kindergarten Cop royalties alone should be enough to cover $79k.
Despite those two advantages, the IRS did file a lien in May for $79,064 that relates to 2004 and 2005, according to TMZ.

The claim by the Governor’s minions is about what you would expect them to come up with: a ‘paperwork snafu.’ In all fairness, the code section cited on the lien is 6721 which, as Tax Girl notes, is informational in nature:

Section 6721 deals with information returns, not taxes owed…Information returns would include such ordinary forms W-2, W-3, 1099, 1096, etc. If that’s the case, it could likely be related to household employee payroll taxes (household employees would include workers such as housekeepers and nannies). However, Schwarzenegger’s office is strongly hinting at the fact that it’s more removed than that – but then, they are politicians.

The other possibility that’s being floated around is that Ahnuld is “listed as a ‘responsible person’ by a business in which he is involved, possibly with a group of partners, and that the IRS might file liens against all of the business’s designated agents,” and thus, “might explain why Schwarzenegger may not have been aware a lien had been filed.”
So, as usual, no one really knows anything for sure and nobody is talking. The man has been a failed state to run people, he can’t be expected to be on top of everything.
Schwarzenegger’s Office Blames $79,000 Tax Lien on ‘Paperwork’ Snafu [Mercury News]
The Governator Blames Tax Lien On “Snafu” [Tax Girl]
See also: IRS Files $79k Tax Lien Against Gov. Schwarzenegger [TaxProf Blog]