Hi,
It seems that "bookstore1" project (web application), is importing the "dist/bookstore.jar" from another project (persistence unit?). In this case, NetBeans will also try to recompile the project's dependencies (other projects that may also require "TopLink Essential" library in the compiler's CLASSPATH).
I think you should open the other project (manually or right click the web project, and select "open required projects" option), and edit its properties to also add the "TopLink Essentials" library to the compile-time libraries (in the "libraries" category).
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