Many plan sponsors get into trouble in their role as retirement plan fiduciaries because they make common mistakes that can get them in hot water, according to Ary Rosenbaum, an attorney in Garden City, New York, who specializes in ERISA issues.

Many plan sponsors don't hire financial advisors because they believe they can do everything themselves but, according to Rosenbaum, the role of a retirement plan financial advisor is not just picking investments. It is drafting investment policy statements and providing financial education to employees.

"When it comes to most retirement plans (especially participant-directed 401(k) plans), participants are actually paying the plan expenses. The problem? A plan sponsor has fiduciary duty to pay reasonable expenses, especially when the participant is footing the bill," he said in his most recent article, "Errors that Retirement Plan Sponsors Should Avoid but do Anyway."