Importprivkey problem for Litecoin clone

I have cloned an older version of Litecoin using a tutorial. I chose the starting letter for the public addresses to be lower case “x”. Everything is working fine except for importprivkey. It will always gives error 5 wrong format. I tried using paper wallet generated keys (paper wallet generated private keys starting with addreses K,L and J) while the windows-qt wallet dumprivkey dumps private keys starting with nr 2 but that can not be imported as well. Is it because of letter x? FYI I have compiled a clone using letter “L” (same like Litecoin) and everything works so i doubt there is a coding error.