Oracle Linked Server only works with Sql Login

I'm having this weird error for some time.

When I login to sql server and use the linked server

SELECT * FROM OPENQUERY(MEGA, 'SELECT 1 FROM DUAL')

I receive this error

OLE DB provider "OraOLEDB.Oracle" for linked server "MEGA" returned message "ORA-01017: senha/nome do usuário inválido; log-on negado". Msg 7303, Level 16, State 1, Line 2 Cannot initialize the data source object of OLE DB provider "OraOLEDB.Oracle" for linked server "MEGA".

One must think it's a username/password error but when I recreate my linked server login it still doesn't work, only for a non Windows Authentication login (aka SQL Login)