Talks between the Bangladesh government and the Tata group on its proposed $2.5 billion investment in the country have failed to make any headway.Alan Rosling, executive director of Tata Sons, said they would now send a revised proposal package to the government in the next 15 days in the light of the differences in the past six months of negotiations.Officials familiar with the negotiations said government negotiators have left the matter to policy-makers as the two sides could not agree on crucial issues of gas pricing, sovereign guarantee for gas supply and committing certain gas fields for the Tata projects.Talks have been on between the two sides for the last six months on the Tata group's proposal to build steel, power and fertiliser plants in Bangladesh.