I ran a few tests and I have a few answers, though not all of them are elucidating.
Portable version was failed to update - File not signed.
This looks like a common issue with this release. The file signature passed all checks and the issue seems to occur only when it is downloaded from a server. I've traced it to an issue where files downloaded from the internet fail the signature check in IE (Dragon uses the same method of validating file signatures).
It's not easy to test since it has a relative reproduction rate of 1 in 50 on our systems.
[2013-11-12 23:01:04|8916|WARNING] Failed to create directory C:\\first_launch_portable
I've managed to reproduce this issue by mapping "Program Files (x86)" to a different drive, which seems to be the case on your system (please correct me if I'm wrong). It doesn't look like the functionality is affected though, the "first_launch" file and folder are created and deleted normally. We'll investigate why the application logs a warning message and hopefully get some insight on other related scenarios.
After the fresh installation I recived a message: "Whoa! Comodo Dragon has crashed. Relaunch now?"
This issue didn't reproduce at all. It looks like the user profile got corrupted during installation. Also, there seems to be no connection between the warning message in the log file and this crash.
If you have any details that could hint to the cause please share them (details like: command line parameters that you launch Dragon with, the exact steps you took to install the last version).