Naples, March 4 - Ex-premier Silvio Berlusconi is unable to appear before prosecutors in Naples in a bribery probe on the dates they have request - but he can meet the following week, ANSA sources said Monday. Berlusconi, who is being probed in relation to alleged bribes paid to a Senator to switch sides, cannot meet on March 5,7 or 9 but instead can be interviewed by investigators on March 15, the sources said. Last week, judicial sources said Berlusconi wass being probed in Naples for allegedly paying three million euros to Senator Sergio De Gregorio to switch sides from the centre-left to the centre-right. De Gregorio, who prosecutors say admitted last week to receiving bribes, defected from the left during Romano Prodi's 2006-2008 government and eventually joined Berlusconi's party. "The deal was made in 2006," Naples prosecutors quoted De Gregorio as saying. Prosecutors said De Gregorio came forward with the allegations in December. The case is only the latest of a series of legal headaches for Berlusconi, whose centre-right alliance did better than expected in last week's general election. Last week, prosecutors in the northern city of Reggio Emilia said they had opened a probe into a letter Berlusconi sent to millions of Italians before last week's election, about a promise to pay back the IMU property tax. Berlusconi was accused of attempting to buy votes with that pledge by rival politicians, who complained the letter was deceptive as it looked like an official document informing people about how to obtain a rebate, rather than an election pamphlet. Rome prosecutors are also investigating after a similar petition. Berlusconi is also on trial in Milan over accusations he paid for sex with an underage Moroccan dancer, and is accused of abuse of office in the same case. Berlusconi is appealing against a one-year conviction he was handed last year for tax fraud on film rights for his Mediaset TV group.