Shared jar in WEB-INF/lib not being found

Hi guys. 

I am new with Appian and have being struggling in some basic things. 

I am writing a very simple plug in only for testing purposes which access a class X which belongs to my personal library. I shared the jar containing this class inside $APPIAN/web.war/WEB-INF/lib folder. 

I removed the jar from META-INF/lib of the plug in structure. Thus, the resulting plug in jar is smaller and is relying on the jars present in WEB-INF/lib.

It turns out that when I deploy the plug in, I got a "Missing Class" message for the X class.

What am I doing wrong? Isn't WEB-INF/lib the right place to place shared libraries in the server?

Any help on this will be very appreciated. 

Thanks!