Dynamic extensions

While hacking  Eclipse to create a dynamic extension, I  run into following error:

Unauthorized access to the ExtensionRegistry.addContribution() method

I googled for the answer, but to no avail. Fastest way  to find what's causing this was, as usual,  to read sources of  Equinox Registry plugin, where checkReadWriteAcess method returns true only if token equals to master token or it's user token, and contribution is not persistent. ( i.e. third argument of addContribution is set to false )