A Palmer casino development group filed suit Thursday against Springfield businessman Peter Picknelly and Penn National Gaming, contending that Picknelly’s 2008 investment in the Palmer casino effort prohibits him from joining Penn in a competing project. Picknelly, who has maintained he is no longer involved in the Palmer project, is a partner in a proposed $807 million Penn National casino resort in Springfield. The lawsuit by Northeast Gaming Group says that Picknelly invested $500,000 in the effort to bring a casino to Palmer, in return for a share of Northeast’s profits if it is successful. The suit accuses Picknelly of breaching the deal. Picknelly and Penn National said in December that Picknelly has no obligation to any other casino effort.