I notice a similar report here:
https://lists.fedoraproject.org/pipermail/arm/2013-December/007127.html
but no solution.

Whiteboard: (none) => MGA4TOO

Seems that hitting CTRL/c during the hang allows the program to continue:

^C                                                                                                                                         
[baz@jackodesktop ~]$ Error creating proxy: Address element 'needed' does not contain a colon (:) (g-io-error-quark, 13)                   
Error creating proxy: Address element 'needed' does not contain a colon (:) (g-io-error-quark, 13)                                         
Error creating proxy: Address element 'needed' does not contain a colon (:) (g-io-error-quark, 13)
Error creating proxy: Address element 'needed' does not contain a colon (:) (g-io-error-quark, 13)
execute:['/usr/bin/python', '/usr/sbin/fedora-arm-installer', 'd', '/var/tmp/faii.d.log.9grs3d', '/var/tmp/faii.d.bin.sHy0WC']|[]
execute:['/usr/sbin/fdisk', '-l']|[]

The GUI then works.

Another launch and CTRL/c managed to produce:

[baz@jackodesktop ~]$ Traceback (most recent call last):                                                                                   
  File "/usr/sbin/fedora-arm-installer", line 815, in timercall                                                                            
    def timercall():                                                                                                                       
KeyboardInterrupt                                                                                                                          
fedora-arm-installer

OK this is fixed in fedora-arm-installer-1.1.1-4.mga5.noarch.rpm.
I have removed a hard coded URL which was causing the hang, waiting for network to time out.
The "download" button is inoperative until upstream decide to do something about this, however it does not impact on the main function of creating a boot device from a local image file.

Update Advisory

fedora-arm-installer-1.1.1-3.1.mga4 is now in /4/updates-testing

This removes the delay on launch which was being caused by an obsolete URL. Since there is currently no server to provide the correct files, I have disabled the remote (download) feature, so the "Download" button is inoperative. This is now mentioned in the description

Testing:
Install (or update) to the version in updates/testing,
Launch the application and check that you can immediately use the browse feature to select an iso to write to a usb stick or SD card.
Instert a usb stick (<= 32GB) 
Click "Install"
On completion check that the device boots.

Files affected:
fedora-arm-installer-1.1.1-3.1.mga4.src.rpm
fedora-arm-installer-1.1.1-3.1.mga4.noarch.rpm

Hardware: x86_64 => All
QA Contact: (none) => qa-bugs
Severity: major => normal

I have tested in Mga4 x86_64 and it now works OK.

Whiteboard: MGA4TOO => MGA4TOO x86_64OK

Barry, you forgot to assign this to QA.  I'll do it now.

Advisory in Comment 4.

Version: Cauldron => 4
Assignee: bugsquad => qa-bugs
Whiteboard: MGA4TOO x86_64OK => MGA4-64-OK

Oops sorry - thanks

Tested successfully and verified the fix on Mageia 4 i586 as well.

Validating.

Could someone please upload the advisory in Comment 4?

Sysadmins, once the advisory is uploaded, please more to core/updates.  Thanks.

Keywords: UPSTREAM => validated_update
QA Contact: qa-bugs => (none)
Whiteboard: MGA4-64-OK => MGA4-64-OK MGA4-32-OK
CC: (none) => sysadmin-bugs

Advisory uploaded.

Whiteboard: MGA4-64-OK MGA4-32-OK => MGA4-64-OK MGA4-32-OK advisory

An update for this issue has been pushed to Mageia Updates repository.

http://advisories.mageia.org/MGAA-2014-0201.html

Status: NEW => RESOLVED
Resolution: (none) => FIXED