sparsebundle problem-unable to mount - OSStatus error -6602

Here's another thing:
I just logged back in to the ReadyNAS via AFP but using admin as the user again and checked the size of the sparsebundle there which comes back as 551.29GB which is probably about right - both drives in the DUO are 1.5TB (actually more like 1.36TB).
The rest of the drive space I use for current and ongoing work data.
Now there is another 199GB left of space and it seems that this is what TM in frontview is trying to use to write a new sparsebundle to but is failing but won't let me change the capacity from 0 to the 190GB max it shows.
However if I actually turn on TM on the mac and choose change disc I have several options including admin which tells me I have 199 GB space to set it up in.
Now for me the best thing would have been just to set it back to the sparsebundle from before but for some reason I can't get TM to connect with this?!!??
If I try running TM from the mac logged in as admin then it goes through the "preparing" stage for ages but now it suddenly seems to be working!!!!

It's still got a way to go but I'll report back when/if it completes.
The only thing is why is setup like this and can I change it to work as it should? - as in being in the correct folder?
As I've mentioned, on the imac it's logged into the DUO via TM as admin and is effectively writing to a folder called admin, however in frontview the username which I can't change (under Backup>Time Machine) is ReadyNAS which I can't seem to enable properly, as it won't let me set anything but 0GB of a max 190 Capacity.

Also under CIFS I can see an iMac.sparsebundle folder that when i click on I get the message "The operation cannot be completed beacause the original item for "iMac.sparsebundle" cannot be found."

Okay, it works, in a sense, but not how it should, which worries me.

Any clues as to how I transfer this admin TM backup to a RedyNAS signed in directory?

Thanks.