Installer freezes/hangs while extracting data

I'm using the pre-built 2.0.0 installer provided on your website (since I didn't want to rebuild Qt statically).

I've created an installer with two components. The first component is the root one, it contains some 7zipped data and a script to install a start menu shortcut. The second contains some more 7zipped data, and a script to change the extracted dir and add an execute operation to run a program after extracting.

On my development machine the installer works perfectly. I copied the installer to a USB key, checked the checksums to make sure it copied correctly (thought it was copying incorrectly at first) and then try to run it off of the usb key on the test machine.

The test machine is a fresh install of win7. It doesn't have any Qt components installed. When I run the installer it goes through the menus fine, brings up the UAC elevated prompt, etc. When it gets to the actual install part it will go through some of the files then hang. It usually doesn't get past the first components files. It seems to be using a bit of CPU but nothing major (~3%). I can see that some of the files will have been extracted to the Program Files dir, but the last file it's stuck on will have 0bytes.

I tried moving the installer from the USB key onto the machine itself and for some inexplicable reason it will get farther. It got past the first component once (installing the start menu shortcut) but got stuck on the second.

I'm running avast antivirus on both machines. On the dev machine it didn't warn me or bring up any prompts. On the test machine, when running from the machine itself (and not the USB key) it brought up a prompt saying it was scanning the installer and then said it was OK, prior to letting the installer launch. I turned off the shields just in case after that.

I'm going to try changing the compression method to store to see if it's something to do with the 7z archives. I've already removed the second component and the script to create a start menu shortcut, neither of those actions fix it.

And the last time I ran it on my test machine the installer crashed. I have no idea why the behaviour changed this time... Also no idea why moving it from the USB key changes anything...

Is there anything I can do to debug this? Console output perhaps?