If you are having the issue where you have duplicate mods when launching a modpack please follow the following guide. It should fix the issue you are having.
Re-install FTB
Step 1:
Open the launcher > click options and copy the install folder location.
Step 2:
Go to where you installed FTB to and delete everything within the folder.
Step 3:
Press the windows button + R at the same time.
In the box that shows up enter: %appdata%.
Step 4:
Find the folder named ftblauncher and delete it.
Step 5:
Launch the launcher and install the modpacks you want.
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If you continue to have errors pastebin the console log here while in debug mode.
Re-install FTB
Step 1:
Open the launcher > click options and copy the install folder location.
Step 2:
Go to where you installed FTB to and delete everything within the folder.
Step 3:
Press the windows button + R at the same time.
In the box that shows up enter: %appdata%.
Step 4:
Find the folder named ftblauncher and delete it.
Step 5:
Launch the launcher and install the modpacks you want.
===================================
If you continue to have errors pastebin the console log here while in debug mode.