The alias can't be opened because the original item can't be found

I have a G-RAID2 drive connected to my time capsule by USB. I use it for time machine backups. It backs up no problem and I can also restore from it. The TC is connected to my iMac by Ethernet.

My problem is that if I try to access the G-RAID2 drive in the finder on my iMac the drive is mounted onto my desktop but i get a message telling me that 'The alias "G-RAID2" can't be opened because the original item can't be found." and I am asked to delete or fix the alias.

If I connect to the time capsule from my MacBookPro using Airport I can mount the G-RAID2 and view the contents!

Can anybody tell me why I cannot access the G-RAID2 drive from my iMac? I have tried repairing the disk in Disk Utility, I have tried fixing the alias (but I cannot select the drive) and I have tried deleting the alias, without any success. I have also tried connecting the drive directly to my iMac but I still have the problem.

I hope somebody can help!