Time Machine backup to AEBS with ext HDD not working for one system

mods, if have posted in wrong forum please feel free move.

searched on , not find else experiencing this. here goes-

got great deal on 2tb wd usb hdd last week take advantage of time machine connected our airport extreme base station. have 4 computers total use backup (2009 13" macbook pro, 2007 macbook 2.0, , 2 dell mini 9s running snow leopard).

more specs- airport extreme 802.11n (2nd generation) running firmware 7.5.2 (latest).

first mistake made going around usb hdd , backing via time machine each one. found out if want network backups have start there. reformatted , started over. first did 2 mini 9s since didn't have data on them. went try macbook pro , received following error-

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went on , continued backups other 3 systems, of work fine. whatever reason macbook pro refuses work. can confirm access drive because can read , write network. seems time machine on system has issue. did notice macbook pro machine updated 10.6.8 far. perhaps has it?

has come across issue before? know how fix it? understand process not support apple find strange works on 3 machines not one. i'll update macbook 10.6.8 , see happens if has ideas in meantime appreciate it.

 

i wanted bump , add performed reinstall of operating system. before migrated data other backup, time machine work fine usb hdd attached aesb. once migrated data though, issue returned. on appreciated. there plist file or can remove , regenerate time machine?

 

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