Could not load class - JDBC

I'm trying to get a JavaEE project to run on Glassfish 4.0 but when I try to flush inserts (persist) to the Sql Server DB it throws this error:

org.omg.CORBA.MARSHAL: WARNING: 00810057: Could not load class com.microsoft.sqlserver.jdbc.SQLServerException  vmcid: OMG  minor code: 57 completed: Maybe

The connection works in Netbeans for running commands and generating entity classes.

Bean method:

    public int addUser(UserDetails u) {
    try{
        User uP  = new User(u.getUserName(), u.isEnabled(), u.isAdmin());
        em.persist(uP);
        return 0;
    }
    catch(Exception e)
    {
        throw new EJBException(e);
    }
}

Persistence.xml:

<?xml version="1.0" encoding="UTF-8"?>
<persistence version="2.1" xmlns="http://xmlns.jcp.org/xml/ns/persistence" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/persistence http://xmlns.jcp.org/xml/ns/persistence/persistence_2_1.xsd">
  <persistence-unit name="LibraryBeanPU" transaction-type="JTA">
    <jta-data-source>JavaEE_Library</jta-data-source>
    <exclude-unlisted-classes>false</exclude-unlisted-classes>
    <properties/>
  </persistence-unit>
</persistence>

Client:

    public static void main(String[] args) {
    LibraryClient lc = new LibraryClient();
}

public LibraryClient()
{
    LibraryFacadeRemote request = (LibraryFacadeRemote) getEJBBean("LibraryFacade");
    request.addUser(new UserDetails("admin", true, true));
}

public Object getEJBBean(String beanName) { 
    try {
        InitialContext ctx = new InitialContext();
        return ctx.lookup(beanName);
    } catch (Exception ex) {
        System.err.println("ERROR: while locating bean from the server " + ex.getMessage());
        return null;      
    }
}