Problem with Time Machine not Mounting

[Siron]

Okay here's what I have. My MBA connects to my external Time Machine drive (a DROBO) through my Mac Pro (the TM drive is connected to the MP with a USB 2 cable). My MBA connects to the MP through my WiFi 80211n router. I have no problems with the WiFi connection to my MBA.
I have had no problems for the last nine months or so but for the last month or so I have not been able to do backups as it tells me Back Up Failed -- Cannot Mount Drive
If I look to see what disk is used for TM it does not show any. I then go to my MP and in Finder TM shows up (and my MP backs up just fine). I log onto my MBA from the MP as a User -- using the password that I have for it, go back to the MBA and in finder I can now see the TM folder and when I open it I see two Sparse Bundles -- one dated April 2008 (about two months after I got the MBA) and one dated May 2009 (about the last time TM backups worked).
I then go into TM and under Select Disc I can now see the TM disk. I select it and then click on Backup Now but the Preparing Backup takes forever and then fails.
I called AppleCare but as the TM drive was not connected to the MBA they said they couldn't help as it was a network problem.
Can anyone help me get TM working again? Do I have to delete all the sparse bundles and connect the TM drive direct to start all over again?

 

[Siron]

Surely someone can help me with this???

 

[Shuttleworth]

Is the TM drive on the Drobo still set up as shared on your MP ? If it's changed that could be your problem. Also , can you mount the TM drive on the MBA desktop then try doing a backup?

Are you sure you're not looking at the MP TM backups

Also what happens if you select the TM sparsebundle but instead of starting a backup, try and enter Time Machine, does that still work? If so, you could just start a new TM backup as of now, and if you ever needed anything from the old one, you just change back to the old TM sparsebundle.

 

[Siron]

Thanks for the reply. TM is mounted on the MP. I can navigate to TM folder from the MBA. I got tired of screwing with it and so deleted the Sparesbundle and now TM works (after 5 hours of creating a new backup).