What you have done should work, as witnessed by numerous people in the thread :
Using Lync 2010 client in Office Communications Server 2007 R2 environment.
However, there seem to be several possible gotchas, having to do with older installations of OCS on the same computer.
A guy named haytham in the above thread found that :
I solved the problem and it work fine now, what i did is installed the
old ocs client, do the registery changes then installed the lync
client then it works :)
in the beginning i was uninstalling the old client before install the
new and was not working i think it need to not unistall the old ocs
2007 client just upgrade it to new ver.
I suggest to read carefully the thread and all comments to try and see what the problem is.