Time Machine failed backup

I recently replaced bad hdd and have restored all my files. TM now says;

This backup is too large for the backup disk. The backup requires 770.67 GB but only 319.30 GB are available.

My MAC is 2007 with 320 gb internal, TM is LaCie 320 as well. I have been using this device as backup for years but since my hdd started having problems and i was not able to stop auto backups, it had since overwritten older backups which i think are the good files. I then used disk utility to wipe clean/erase TM, partition 1 for 319gb again.

Since my internal is same size as target drive, where is the large file coming from ?

Appreciate any help from everyone.
Thanks in advance.

It sounds like you may have "ghost" backups remaining on your internal hard drive which have been copied over from the bad hard drive. Although that's just a guess on my part....

Download and run the free Disk Inventory X to see what's really going on with your hard drive. If possible, post a screen shot for us to look at.

Thank you, chscag !

I did find what was causing the rather large file; i found a post for checking options in TM which i have checked a few times already. What confuses me is TM options did not list my 2nd xhdd w/ 2 partitions. Here's a rundown of what i did :
- opened TM in system preference
- clicked options
- clicked + sign to exclude files (only listed time machine)
- ehdd1 showed in list
- clicked again to add ehdd2
- time machine is grayed out but but ehdd1 & 2 are not
- exclude the 2 ehdd

TM finally ran and did not stop. i checked this morning as a was away at work and it completd with no errors. i don't like the logic there with the option of adding the volume/drive or files when its not listing. If its not listed then TM should not be counting those for backups.

Anyway, problem solved. i did download disk inventory and will use it later to check all drives.

Many thanks also to all advise and recomendations posted in this forum, your all a big help.