In late 2006, the anime Sgt. Frog was licensed by ADV Films. Seeing its potential as a hit on the children's show market, as the anime boom was dying out Sgt. Frog had the potential to kick it into full swing again.
The U.S. release was originally delayed because of these negotiations; ADV even began working with people from Summit Entertainment, who were behind the 4Kids dub of Pokémon, in order to get the show on the air.
It is unknown how many episodes were exactly dubbed (some say only a pilot was made, other says up to three episodes were made), however the episode(s) were dubbed three times; an otaku/fan pilot (similar to the FUNimation dub seen today), a mass-market pilot, and a kid-oriented pilot. Cartoon Network liked the mass-market pilot while Nickelodeon liked the kid-oriented pilot.
However, due to financial troubles ADV was having at the time leading up to their demise, the rights were transferred over to FUNimation Entertainment in 2008, who seemed to have no interest in pursuing a TV deal for Sgt. Frog. (Their dub contains several instances of risque content the original Japanese and ADV dubs did not, making it hard to sell to a children's network.)
At one point, a script containing both the original Japanese-translated lines and one of the pilot's lines for episode 13 of the series was online; however, the script has now gone missing as well.
There were several notable changes in the original dub, mainly characters being renamed. For example, all of the Keronian characters had the third syllable in their names removed; in this case, Keroro became Kero, Tamama became Tama etc. The names of the human characters were also changed; to date, the only confirmed change is Natalie or Nathalie, the English name for Natsumi. When the FUNimation dub was made, all characters retained their original Japanese names.