Scott at Powerline, notes that Al Franken's accountant, who Franken claims is responsible for his failure to pay various state taxes, refused to comment saying he'd been told to say "No comment." Scott implies that this is part of a cover-up.
That's quite unfair to the accountant. Regardless of whether Franken told him not to comment or not, it's almost certain that his accountant is ethically and legally bound not to disclose any information about Franken's tax situation without Franken's express permission. The AICPA, of which most accountant's are members, has a code of conduct that forbids releasing this type of information. Likewise, many state boards of accountancy expressly forbid releasing this type of information. Further, most firms I'm aware of have express policies forbidding disclosure. I would no more expect an accountant to publicly comment without permission on a client's tax troubles without permission than I would his attorney. It's true clients typically do allow their attorneys to speak out in high profile cases, but attorneys have training in making their clients look good to the public, while accountants generally don't.
On another note, I've certainly had clients who received poor advice from former accountants about state tax filings so his explanation is plausible. I've also had lots of clients who never bothered to tell me they were doing business in other states.