make sure the card is securely installed. maybe remove it and place it in an adapter to make sure your pc sees the files on it,and make sure its formatted FAT32.
biggest suggestion: DONT USE ROM MANAGER other than to initially flash clockwork recovery. rom manager is not a reliable way to make and restore backups,do wipes and flash roms,IMO. things can happen... the results vary from bootloops to semi-functional roms with no rom manager and no market to obtain it. in order to fix these things you need a knowlege of manually flashing and restoring in recovery.
my very strong advice: become comfortable booting into clockwork recovery and using the menus there to make backups,do wipes,and flash roms. after youre 100% comfortable with this method,if you still feel the need to use rom manger(for whatever reason
) then go ahead... but at least youll understand what you need to do to recover from a rom manager mishap
the absolute fastest and safest way to get a new rom to your phone IMO:
-donwload to pc. check md5 when available
-transfer to phone via usb cable
-boot to CW and make backup,wipe,install rom
-reboot
-enjoy
my 2 cents,for what theyre worth