This is my working code:

I call it with parameters:

"https://clm.example.com:9443/jts" "adminID" "adminPasswd" "userToDeleteLicense" "com.ibm.rtc.developer-iep.floating"

I use ILicenseAdminService as you did above. Note, it apears NOT to be a typical ClientLibrary, so you need to get it with the code you show in your original question.

/*******************************************************************************
 * Licensed Materials - Property of IBM
 * (c) Copyright IBM Corporation 2008. All Rights Reserved. 
 *
 * Note to U.S. Government Users Restricted Rights:  Use, duplication or 
 * disclosure restricted by GSA ADP Schedule Contract with IBM Corp.
 *******************************************************************************/
package com.ibm.team.workitem.ide.ui.example;

import org.eclipse.core.runtime.IProgressMonitor;
import org.eclipse.core.runtime.NullProgressMonitor;

import com.ibm.team.repository.client.ITeamRepository;
import com.ibm.team.repository.client.ITeamRepository.ILoginHandler;
import com.ibm.team.repository.client.ITeamRepository.ILoginHandler.ILoginInfo;
import com.ibm.team.repository.client.TeamPlatform;
import com.ibm.team.repository.client.util.IClientLibraryContext;
import com.ibm.team.repository.common.IContributor;
import com.ibm.team.repository.common.ILicenseAdminService;
import com.ibm.team.repository.common.TeamRepositoryException;

/**
 * Example code, see
 * https://jazz.net/wiki/bin/view/Main/ProgrammaticWorkItemCreation.
 */
public class LicenseDelete {

	private static class LoginHandler implements ILoginHandler, ILoginInfo {

		private String fUserId;
		private String fPassword;

		private LoginHandler(String userId, String password) {
			fUserId = userId;
			fPassword = password;
		}

		public String getUserId() {
			return fUserId;
		}

		public String getPassword() {
			return fPassword;
		}

		public ILoginInfo challenge(ITeamRepository repository) {
			return this;
		}
	}

	public static void main(String[] args) {

		boolean result;
		TeamPlatform.startup();
		try {
			result = run(args);
		} catch (TeamRepositoryException x) {
			x.printStackTrace();
			result = false;
		} finally {
			TeamPlatform.shutdown();
		}

		if (!result)
			System.exit(1);

	}

	private static boolean run(String[] args) throws TeamRepositoryException {

		if (args.length != 5) {
			System.out
					.println("Usage: LicenseDelete     ");
			System.out.println("  for example 'bob' ");
			System.out.println("  for example 'com.ibm.team.rtc.developer' ");
			return false;
		}

		IProgressMonitor monitor = new NullProgressMonitor();
		String repositoryURI = args[0];
		String userId = args[1];
		String password = args[2];
		String licenseuser = args[3];
		String licenseID = args[4];

		ITeamRepository teamRepository = TeamPlatform
				.getTeamRepositoryService().getTeamRepository(repositoryURI);
		teamRepository.registerLoginHandler(new LoginHandler(userId, password));
		teamRepository.login(null);

		
		ILicenseAdminService licAdin = (ILicenseAdminService) ((IClientLibraryContext) teamRepository).getServiceInterface(ILicenseAdminService.class);
 		IContributor licenseUser = teamRepository.contributorManager().fetchContributorByUserId(licenseuser, monitor);
        licAdin.unassignLicense(licenseUser, licenseID); 


		teamRepository.logout();

		return true;
	}
}

Fascinating and you are right. The LicenseAdminService does not seem to be a regular client library and getClientLibrary does not work.

This code works for me:

		ILicenseAdminService licAdin = (ILicenseAdminService) ((IClientLibraryContext) teamRepository).getServiceInterface(ILicenseAdminService.class);
 		IContributor licenseUser = teamRepository.contributorManager().fetchContributorByUserId(licenseuser, monitor);
        licAdin.unassignLicense(licenseUser, licenseID); 

Where the user licenseuser is the ID as string, and licenseID is something like "com.ibm.team.rtc.developer".

I got the licenseID's this way:

	/**
	 * Build the license map only once
	 * 
	 * @param licenseService
	 * @param monitor
	 * @return
	 * @throws TeamRepositoryException
	 */
	private static HashMap getLicenseMapper(
			ILicenseAdminService licenseService, IProgressMonitor monitor)
			throws TeamRepositoryException {
		if (fLicenseMapp != null) {
			return fLicenseMapp;
		}
		fLicenseMapp = new HashMap();

		IContributorLicenseType[] types = licenseService.getLicenseTypes();
		for (IContributorLicenseType iContributorLicenseType : types) {
			// System.out.println("Lic:"+iContributorLicenseType.getId()+" " +
			// iContributorLicenseType.getName() + " " +
			// iContributorLicenseType.getProductName()+ " " +
			// iContributorLicenseType.getEditionName() +" " +
			// iContributorLicenseType.getDescription());
			fLicenseMapp.put(iContributorLicenseType.getId(),
					iContributorLicenseType.getProductName() + " "
							+ iContributorLicenseType.getName());
		}
		return fLicenseMapp;
	}

Dependent of this being a client side automation or a server extension the call to get the license manager would be:

Client API:

        ILicenseAdminService licAdin = (ILicenseAdminService)teamRepository.getClientLibrary(ILicenseAdminService.class);
        licAdin.unassignLicense(contributorHande, licenseId);

Server API (assuming you extend AbstractService):

        ILicenseAdminService licAdin = this.getService(ILicenseAdminService.class);
        licAdin.unassignLicense(contributorHande, licenseId);


Provided the license ID would be valid, I would assume that this works.