How to resolve Fat Jar Export: Could not find class-path entry

Question

I’m having serious problems exporting a program made in Eclipse and I’m starting to hate myself for trying to be organized.

I imported two third-party libraries (Javamail and iText 5) into my project. Their Jars I downloaded from the Internet and saved in my Downloads folder. I imported the Jars (in the case of External Jars) from Build Path... and everything was working. The program was running perfectly and I was succeeding in all exports.

But then I tried to be organized... I moved the Javamail JAR (which had no folder) and the iText folder - everything - into my Project folder. I did not put either into the /src or the /bin folder, just into the Project folder. To get even more organized, I created a /lib folder inside my Project folder and put these libraries there.

That is to say:

- PASTA DO PROJETO
--- src
--- bin
--- lib
------ JavaMail.jar
------ Pasta do iText com os seus respectivos JARs

I understand that tampering with the destination of these files, after being imported, can cause serious problems. So I didn’t think twice: I went to Build Path..., I deleted libraries (imported from the old Downloads folder), and re-imported them from the new /lib folder.

Apparently all right... The program runs perfectly. Everything works as before. Including the methods for the Javamail and iText libraries.

Only that...

When I export the program (by Runnable JAR file), the following error appears for ALL External Jars:

Fat Jar Export: Could not find class-path entry for [library path]

This does not prevent exporting. It happens normally. But when I open the generated JAR, it shows an error and closes.

What is missing here?