rpm package shows Failed dependencies even though it is present in /usr/lib (by the way, the library is IUP) this is the error error: Failed dependencies: libiup.so is needed by <package-name>
It sounds like the library was installed without RPM (e.g. a manual make install). That can be verified by asking the database rpm -q --whatprovides /usr/lib/libyourlibname.so. If it tells you that nothing provides it, then that is why it failed.
The work around would be to do "--nodeps" on the RPM command line. This isn't recommended unless you are sure that it's the correct file.