I have the same problem updating from a clean install. I unistalled Spine (prev 2.1.27 version), downloaded again the 3.0 setup and installed it.
Please i'm in a hurry and I need to get in Spine as soon as possible. Thanks

I am getting the same issue with Spine Professional with clean install.
Spine Trial updated fine from clean install with very same network environment.

Here is what is in the spine.log:

Spine Launcher 3.0.05
Mac OS X x86_64 10.11.2
Java 1.7.0_51 Esoteric Software
64-bit Server VM
Downloading: Spine 3.0.08
Server error downloading update:
java.lang.RuntimeException: Invalid file length: 2627, expected: -1
at tzax.i.run(SourceFile:1088)

[snip]

Same problem. If you manually download the 3.0.08 file that the updater is complaining about you'll see following errors. Looks like the download server has died, not the updater.

[snip]

Exactly same problem here, can't start or update pro, but no problem at all with trial:

Spine Launcher 3.0.05
Windows 10 Pro x86 6.2
Java 1.7.0_06 Esoteric Software
32-bit Server VM
Downloading: Spine 3.0.08
Server error downloading update:
java.lang.RuntimeException: Invalid file length: 2627, expected: -1
at tzax.i.run(SourceFile:1088)

I have just purchsed this software and also encounter this problem! anyone here knows how to fix this bug???? ! I am so depressed!

me too, same problem:
java.lang.RuntimeException: Invalid file length: 2627, expected: -1
at tzax.i.run(SourceFile:1088)

There may be weird server stuff going on. I'm not sure. Nate hasn't replied about it yet.

Is there any way that i can roll back to the previous version?i have a dead line to catch Thanks

If it's an old install, you can put a file in your Spine user folder (%userprofile%\Spine\) and put a text file there named "version.txt".
In the text file, type "3.0.00" or whatever older version of spine you know you had, and save it. Then run Spine.
Rollback to older version still possible?

Sorry guys, server had an issue while I was asleep. Fixed now!