First, I would download the latest 3.4.1 version and then try to install this version.
Then, make sure you run it with administrative credentials (right click, run as administrator).
Post back if the issue persists.
Thanks for your advice, Mr. McLion.
I downloaded the 3.4.1 version and started the installation as administrator. Unfortunately the same error message occured again.
Then I tried to install the 32-bit version (although I prefer a 64-bit program on a 64-bit operating system). A similar error message appeared at the same point of installation progress, but with another combination of numbers and letters in brackets.
Hmmm .. some users reported problems when they where not the owner of the folders involved. I would also try to deactivate the anti-virus scanner and run from a local drive - just further ideas. Try to reinstall .NET, but not only version 4 as you already did. I'd also try to reinstall 3.0 and 3.5. I'm kinda running out of ideas ..
I am running LR 3.4.1 64-Bit on W7 64-Bit myself - OS language German and LR varying German or English.