You are preparing a new set of shared libraries in /usr/local/applib and you have written and compiled some code that uses these libraries.
You have already performed ldconfig, however the system still cannot find the shared libraries.

What is most likely the cause of this?

A.
You used the wrong compiler.

B.
You did not update your PATH variable.

C.
You compiled the code with wrong library.

D.
You forgot to put the library path in ld.so.conf

Explanation/Reference:
ldconfig reads the file /etc/ld.so.conf and builds the shared library cache for the loader ld.so.
The PATH variable has no influence on the libraries (LD_LIBRARY_PATH does).