while turning off plugins i got this error, i uninstalled 4.15 and reinstalled it. Is there a way to re download or re add the .dll file? The error i am getting is below also.
You can enable OnlineSubsystem manually by editing your .uproject file
{
"Name": "OnlineSubsystem",
"Enabled": true
},
{
"Name": "OnlineSubsystemUtils",
"Enabled": true
},Thank you for the answer Tonicnet, i had already moved my content files to a diff project, and redid all my settings there. I had kept this Question here as an off chance it will help someone else and me if this happens again 
Thank you so much. it work !!