I get HTTP 401 errors when trying to install software I bought. How to fix it?

This can be caused by a couple of things. First, check to make sure you don't have a local configuration error on your computer. To do this, you will need to remove potentially-broken authentication data from your subscriptions.

Local configuration clean-up

The first step is to remove old data from /etc/apt/auth.conf . Open it up as the superuser with a text editor. Normally, you can do this by pressing Alt-F2 (or running a terminal) and running this:

• gksudo gedit /etc/apt/auth.conf

With that file open, you will need to remove the clauses for the package which isn't working, then save the file. For example, let's say your file looks like this:

  machine private-ppa.launchpad.net/commercial-ppa-uploaders/amnesia/ubuntu
  login myname
  password mYPasSwORd1

  machine private-ppa.launchpad.net/commercial-ppa-uploaders/bastion/ubuntu
  login myname
  password mYPasSwORd2

  machine private-ppa.launchpad.net/commercial-ppa-uploaders/bastion/ubuntu
  login myname
  password mYPasSwORd3

  machine private-ppa.launchpad.net/commercial-ppa-uploaders/limbo/ubuntu
  login myname
  password mYPasSwORd4

If the broken download is for Bastion (for example), remove both of the middle sections. Afterward, the file would look like this, with no reference to the broken package:

  machine private-ppa.launchpad.net/commercial-ppa-uploaders/amnesia/ubuntu
  login myname
  password mYPasSwORd1

  machine private-ppa.launchpad.net/commercial-ppa-uploaders/limbo/ubuntu
  login myname
  password mYPasSwORd4

Then save the file and quit from gedit.

The second step is to remove old package feeds. This is done by running a command again. As in the previous step, press Alt-F2 or open a terminal, then run the following command (after replacing 'bastion' with the name of the package which isn't installing):

• gksudo rm /etc/apt/sources.list.d/*bastion*

The final step is to try 'File -> Reinstall previous purchases' again in Ubuntu Software Center.