I can't install xojo. When I click install in the software center it's not progressing. In the terminal it's stuck in :

gichan02@gichan02-Latitude-D520:~$ sudo apt-get install xojo
[sudo] password for gichan02: 
Reading package lists... Done
Building dependency tree       
Reading state information... Done
The following extra packages will be installed:
xojo-bin
The following NEW packages will be installed:
 xojo xojo-bin
0 upgraded, 2 newly installed, 0 to remove and 0 not upgraded.
Need to get 209 MB/209 MB of archives.
After this operation, 596 MB of additional disk space will be used.
Do you want to continue? [Y/n] Y
0% [Working]

then after waiting for an hour for progress it says:

Failed to fetch https://private-ppa.launchpad.net/commercial-ppa-uploaders/xojo/ubuntu/pool/main/x/xojo/xojo-bin_2013.41-0ubuntu1_i386.deb Could not resolve host: private-ppa.launchpad.net

So I added apt repository for 'private-ppa':

deb https://ging-giana:[email protected]/commercial-ppa-uploaders/xojo/ubuntu trusty main

Then when I try 'apt-get update':

GPG error: https://private-ppa.launchpad.net trusty Release: The following signatures were invalid: NODATA 2

Then I noticed something the Software Sources:Other software TAB:

Added by software-center; credentials stored in /etc/apt/auth.conf
https://private-ppa.launchpad.net/commercial-ppa-uploaders/xojo/ubuntu

So i go to the '/etc/apt/auth.conf' ,but It cannot be opened and it is not a keyserver.
So i uncheck:

Added by software-center; credentials stored in /etc/apt/auth.conf
https://private-ppa.launchpad.net/commercial-ppa-uploaders/xojo/ubuntu

GPG error was gone.
But then again I found myself at the beginning of the problem.STUCK at '0% [Working]'.

'Xojo' is the only application that I can't install.Any explanation why is it like that?