when i urn bootloader for first time i have problem with stk500 protocol , sync error....
i found when burn my bootloader i must use 16Mhz crystal inserted to target ,
becouse when i burn boot.... i use SKT500 programmer with own clock generator and this makes trouble for sketches after that for uploading sketches . when i put crystal on my skt500 i burn bootloader again everythink look fine
regards from bulgaria :))