This page is the only Google search result I could find for that error message:

failed to load config: could not find option group Litecoin failed to load config: could not find option group Litecoind failed to load config: could not find option group Ltcd

I couldn't figure it out until it hit me that it's not saying that it cannot find that group in the config file but rather saying that it can't find such a group in the binary to match the directive it did find in the lnd.conf file.

In other words, to fix this, remove the following Litecoin config blocks from lnd.conf:

[Litecoin] [Litecoind] [Ltcd]