You did not mention which version did you use. I have tested (Version 4.0.3) on my machine and I can launch multiple instances.
Settings and translation
Thank you very much Sergey! I have uploaded an updated version to include the those files.
Unfortunately there were policy changes since the release of Windows 10, version 1607. Please have a look here for workaround: https://sourceforge.net/projects/signed-drivers/files/com0com/ Please note it is not advisable to Enable Test Mode due to security implications on your system. However if you are a developer and really need to use this software you can use the workaround as suggested on the link above.
You can find the latest Windows build (version 2.7) here.
Gerbv project failed to load when located outside the Gerber files in WIndows
Add init.scm file
Fixed on next release.