It shows an alert dialog when the setup program is in the step "Installing SourceTree".
The dialog tells that:
Source file not found: C:\ProgramData\Atlassian\SourceTree 1.3.0\install\disk1.cab. Verify that the file exists and that you can access it.
I have checked that folder, but no disk1.cab is there. Only a file named "SourceTreeSetup_1.3.0.msi" is in that folder.