A potential $20 million problem for the group behind the "$100 laptop" isn't going away easily.

Ade Oyegbola, an inventor who claims the One Laptop Per Child nonprofit stole his designs for a Nigerian keyboard, recently won a round in a Lagos court. Now this week, Oyegbola is pressing his case in U.S. federal court.

The dispute began last fall. One Laptop Per Child, spun out of the Massachusetts Institute of Technology by Nicholas Negroponte, was sued by Oyegbola's company, Lagos Analysis Corp., known as Lancor.

Nigerian dialects require punctuation marks not found on standard English keyboards, so Lancor developed a keyboard that uses four shift keys to produce the symbols. Oyegbola claims that OLPC bought two of Lancor's keyboards in 2006, then copied the design for its own models intended for sale in Nigeria.

"It was obvious to anybody who looked at it," Oyegbola said Thursday.

Lancor filed a patent lawsuit seeking $20 million in damages in Nigeria, and last month a federal court there rejected OLPC's bid to dismiss the case. The court also extended a restraining order prohibiting OLPC from distributing its laptops in the country.

Separately, OLPC asked a court in Massachusetts, where Lancor also has an office, to clear it of any wrongdoing. This week, that case was moved to federal court, where Lancor filed a counterclaim alleging violation of trade secrets.

A spokesman for OLPC had no comment. When Lancor's lawsuit first emerged, the organization said that as far as it knew, "all of the intellectual property used in the XO laptop is either owned by OLPC or properly licensed."

The keyboard lawsuit is one of a few setbacks for OLPC, which has gotten its laptops to fewer children than it first expected and at roughly twice the originally sought price of $100. Even so, the group now claims to have gotten orders for a half-million machines for children in several countries, including Peru, Uruguay, Mongolia, Rwanda, Haiti and Afghanistan.