Ambassador Rodley said corruption has costs the Cambodian government an estimated $500 million a year.
Thirty-four families from two villages in the lakeside area say they have not received land titles as expected.
Cambodia marked the 10th anniversary of the International Year of Volunteers last week, as officials called on more volunteers.
One of the major points of concern for some NGOs was the mandatory registration process in the original draft.
The report urged more action at the grassroots, rather than national, level, to lessen the impact of climate change.
The law contains punishment of up to five years in prison for the illegal sale and from 15 years to life for convicted assailants.
Poor parents cannot always afford to send their children to school, where low-salaried teachers often ask for bribes.
According to government figures, the literacy rate in Cambodia stands at about 70 percent.
Government subsidies could help, but no such support currently exists.
The group were taught to better use social media last week, as an increasing number of Cambodians become tech savvy.
The two-day training came as Cambodia approved a measure to tighten controls on Cambodian migrant laborers.
As it has in the past, the festival opened with blessings to chase away evil spirits, bad karma and ill luck.
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