Hello Summoners! A lot of us (including me) have experienced the issue wherein the Garena Messenger crashes when we try to launch League of Legends.
Again here are the steps to do a clean uninstall/reinstall of your Garena Messenger (this fix worked for me and for the majority everyone else)
1) Make a copy of your Apps folder first before uninstalling, and paste it in your desktop (Program Files > Garena Messenger > Apps). That way you don't have to reinstall all your games again.
2) Make a clean uninstall/reinstall.
a. Boot your PC in Safe-Mode.
b. Proceed to Add/Remove Programs.
c. Uninstall Garena Messenger (You may also opt to use Ccleaner to uninstall)
d. Delete any trace of Garena Messenger (Folders, Files, etc...)
e. Once done, reboot your PC.
f. Proceed to Normal Mode.
3) Download the latest Garena Messenger installer HERE.
4) Proceed with the installation.
5) Paste your copy of Apps folder inside the Garena Messenger folder. (Program Files > Garena Messenger)
6) Launch Garena Messenger (this should prompt you to update)
7) Go play LoL!
*Note: This fix worked for the majority of those who have experienced this issue
The steps given can also be used to fix the LoL Authentication Time-out error.