The root cause is that the oci.dll file that comes with navicate is not compatible with oracle's oci.dll file.
Your navicate downloaded is 32-bit or 64-bit , just go
http://www.oracle.com/technetwork/database/features/instant-client/index-097480.html
Here download a 32-bit or 64-bit corresponding to the file ,
After downloading, unzip to get these things:
Then open your navicate, find the tool,
After this oci.dll you just unzip the file into the path of the file inside the oci.dll file , then save, reboot navicate to connect oracle.