Backup disk not available...very annoying!

Hi, I'm new to this forum so apologies is this should be posted somewhere else.

Please could someone help me out with this. I have seen another thread similar to this but it seems quite old now and due to software updates and firmware updates that thread seems out of date so thought I'd post a new topic .

I have an iMac and MacBook pro both running the latest lion software. I have a 1tb Iomega hard drive connected to my iMac via USB. The hard drive is partitioned into two partitions of 500gb and time machine on my mac backs up to one of the partitions. This works fine on every backup with no issues.

However the issue is with my MacBook pro. I am wanting to back up to the other partition on the hard drive over my wifi network. I have successfully set up a shared folder on that partition for the backups to be saved in and in the time machine preferences I have successfully selected the folder on that partition to back up to. I can also, if I wish, save files in that folder on the hard drive from my MacBook... with no issues. But...when I run the time machine back up I get the following error:

Backup disk not available

Is there any reason why this is happening and how can I resolve this?

Any help would be much appreciated

Cheers

 

Yea both are and both partitions work fine with my iMac

***can anyone help here?***