[Geoff Bacon]

What version of MSP are you using?
Are you using the companion to backup via Wifi or are you using another mechanism ? If so,  what version?
(Mike will need the e versions)

Sometimes one of the files can cause the backup to fail at the same point each time (unlikely in your case as you did succeed in performing a backup)

Should you get a similar issue in the future, consider performing a local backup on the tablet and manually copying the resultant file to the laptop (you may have done this already). This takes the wifi out of the equation.

Check that you have enough space for the backup on the target device (some people have had issues with the device running out of room and MSP not detecting/handling the issue).
You might want to check that there is at least twice the size of the backup available (in case MSP is using a temporary file).
Also check that the tablet has enough space to hold a backup (in case MSP is creating a temporary file which it then copies to the destination).

I'm sure Mike will be along shortly to help you (and correct anything wrong above).

Geoff