Constantly tinker around within your test environment/sandpit and invariably things will break. Installing and uninstalling Lync 2010 RC and RTM caused a couple  of issues for me.  

For example, I noticed that users previously provisioned in older OCS/Lync setups, that I now wished to re-provision, weren’t appearing in the Lync Control Panel. Possessing an old SIP address from a previous install caused this hiccup.

To clear out stale attributes, launch AD Users and Computers and go into the Attribute Editor (or use ADSIEdit) and find the msRTCSIP-PrimaryUserAddress attribute .. clear any existing value and the user will then appear in Control Panel.

Now the user appears in the search, but then another obstacle, a cannot move user in enable operation error.

This one turns out to be the msRTCSIP-UserPolicies attribute.

Cleaning out this value then allows the user to be provisioned.

If you need to provision an administrator account, that’s something different, down the Powershell route (Enable-CSUser). Those steps have been already well blogged elsewhere on ye ole T’Internet.

Mylo