There's 3 known launchers/installers that exist (excluding Steam for the purpose of explaining this):
1) The really really old beta installer (also used by PGI for installation troubleshooting): It's the one that has a default direct install of Games/MWO or some such. The frontend/launcher is the same one that most people used during the game's launch/debut (aka out of beta).
2) The "standard" installer tends to install to the default Program Files directory (it'll use the Program Files (x86) folder if you are using a 64-bit version of Windows) using the most common launcher (pre-Portal based) that most people had been using previously. This installer was released at approximately the time MWO went out of beta.
3) Portal: Resistance is futile. Chances are if you had used the MWO Tourney Client, you were using this and it eventually got updated when the "official Portal" launch happened (official Portal launch was a year+ after the Steam launch).
Portal (and recent versions of the launcher) uses .NET 4.5.2 as a requirement for it to function (.NET 4.7 is the latest), so... go update that if you are having issues (or just install it through the Portal installer).
If you are using version 1, that will most likely cause certain transitional problems when moving to Portal.
If you are using the Steam version, Portal will NOT detect the Steam version (because the Steam version stores its data in Steam's folders - however player/user data is stored elsewhere and shared by both MWO official client and Steam MWO client data).
You can attempt to copy Steam's version into the standard/defined MWO folders if you understand the structure used by MWO and/or Steam.
Edited by Deathlike, 27 May 2017 - 06:40 PM.