The AWC needs to be upgraded to MCA. The error stating there is a newer client download is a bug because even if you turn off the MCA feature for the UCA feature profile, you will still get that error because your UCA is configured with a collaboration server. The client installs with the collaboration server enabled regardless of your feature profile. The latest release of 4.0.0.25 still has this bug. I just went through this with a new install and Mitel.
For installers out there, if you install UCA and you have MCA, do NOT install the MCA blade on the same server as UCA unless you plan on getting it running. If the blade is installed, UCA still tries to run the collaboration server regardless of features. Also, if UCA and MCA are on the same server, I would suggest that your DN of MAS is the FQDN of MCA. Example:
MAS - collab.domain.com - Locally resolved
MCA - collab.domain.com - Externally and internally resolved and points to internal LAN IP
UCA - uca.domain.com - Externally and internally resolved and points to internal LAN IP
UCA - always build via FQDN and never IP
Once this is done, and users browse to collab.domain.com, they will automatically be routed to collab.domain.com/portal. You can still access collab.domain.com/server-manager internally.