3? M? L? What to do? What does it mean?
Litecoin addresses were closely resembling bitcoin addresses and were changed from the shared prefix of "3" to "M" for LTC - L addresses should work normally.
If your wallet hasn't updated, it will not send to the address however this can be changed as addresses can be converted backwards with this tool.
To deposit if your wallet isn't taking the address provided
(EXAMPLE: MEPJSXs7HCH6yQXwcUsfaTfjeqxYB2DRHG converts to 38BA8eT9L5RgAuG3WbtKkpRLL9N6AQFuRF which should send successfully!)
Using the link above just do the following:
Step 1. Go to https://litecoin-project.github.io/p2sh-convert/
Step 2. Put your deposit address in the box, and click the "Convert" button.
Take the converted address and put that into your wallet, you should now be able to send Litecoin!