just a couple of things to check:
1)that the sd is formated FAT32. this is a must! if its plain FAT,or anything else,PC10IMG will be invisible. if you find a format other than FAT32,youll need to back up the SD and reformat it.
2)make sure its named correctly. the phone must see "PC10IMG.zip",so if you are using windows,wich likes to automatically add and hide the file extention,then you just need to rename to "PC10IMG" as manually adding the .zip,and calling the file "PC10IMG.zp" results in the actual name being "PC10IMG.zip.zip"
in much rarer occasion,if youre using someting other than windows,or just have your PC set differently,naming PC10IMG may result in it just being named "PC10IMG" with no file ext. so if thats the case,you will need to name it "PC10IMG.zip"
you also do need to use capital letters,and that is a number 1,not a capital "I",and a number zero,and not a capital "O",for the third and fourth digits. it may be obvious that the characters are,ands im not trying to insult you,just relaying some things ive seen trip folks up.
id be willing to bet the sd format is whats tripping you up,but check out thise 2 things and see if it wont flash for you then