Shares in 21st Century, a leading supplier of public transport CCTV, fell after it announced the resignation of its Chief Executive and raised questions about meeting expectations this year.The firm said Nick Grimond had resigned his position as CEO for 'personal reasons' and would leave the company on 28 September 2012.The firm was currently trading in line with management's profit expectations but meeting targets depended on several contracts coming through in time."The full year profit expectation is weighted toward the second half of the year and, while the group's current order book and sales prospects support management's expectations for the full year, achievement of these forecasts will depend upon a number of potential contracts being confirmed and fulfilled before the year end," said Chairman Jan Holmstrom. "Regardless of this we expect that the profit for the current year will exceed that achieved last year," he added.The company posted revenue for the first six months of the year of £7m, down from £7.8m in 2011.Pre-tax profits were unchanged at £0.7m and the board said it would consider a dividend.Following the reshuffle at the top, current Finance Director, Wilson Jennings, will take over as Managing Director of the group's main trading company with immediate effect.He will then take on the CEO job when the incumbent leaves.Holmstrom praised Grimond for his role in repositioning the business to focus on public transport monitoring systems and the more recent expansion in mainland Europe. "Wilson is well known and respected by our staff, customers and suppliers and we are confident of a seamless transition into this role and continued momentum in the business going forward," he added.Following the announcements the firm's shares fell 13% by 1030 on Wednesday morning.