If you get a "Cancelled" message when trying to submit a report to Larian, it most likely means that an assembly (specifically the zip file creator) is missing.
Steps to fix:
1) Download the following zip: http://dotnetzip.codeplex.com/downloads/get/258014
2) Copy zip-v1.9/Ionic.Zip.dll from the archive to the game binaries directory (SteamApps\common\Divinity - Original Sin\Shipping or wherever you installed it)
3) Crash upload should work now - at least it worked for me