Time Machine Won't Backup - "sparsebundle is already in use"

I’ve been trying to get my MBL to play nice with my mac, without much luck.  Initially I was getting horrific slowness, (“estimated time (to backup): 59,353 days”) and found a number of tips that gradually edged my speeds to back up 300GB to a more mortally attainable 3 days.  

My speeds dropped again, just as the last 10Gb were backing up, so I took a stab at setting the network setting from DHCP to Static, assigned all the appropriate IP,  Subnet and DNS info and now get a message that it can’t complete the backup as the sparsebundle is already in use.  I’ve tried resetting back to DHCP.  I’ve tried resetting the static IP to the same IP as the last one when it was connected via DHCP.  I’ve tried rebooting between settings changes.  No joy.  

Any suggestions of what I’m doing wrong?

Thanks in advance for any help.

Found a solution, in case this is of use to anyone who encounters a similar issue: 

I’d rebooted the mac, but not my MBL.  Once I did this, it seemed to get back on track.  

You can restart the NAS by going into the Dashboard, then Settings/Utilities/Reboot on the browser user interface.

It’s now backing up, although no idea how long it’ll take as it’s showing the estimated time remaining as “About 5 seconds”…and has clung to this assessment for at least the last 30 minutes!  It seems to have undone whatever was making it backup quicker and t’s back to being grindingly slow…[sigh!]