Vista - Issues with audio calls cause WLM to freeze

I have had this annoying problem ever since I made calls on WLM 8.5. I have
just upgraded to WLM 9 Beta but the problem still persists.

Details of the problem:
- Whenever I answered a call from another contact in WLM 8.5, the moment it
said connection established WLM would freeze. This meant I always had to call
the contact but currently, with WLM 9 Beta, this seems to not happen anymore.
- When calling a contact, if the contact failed to answer or failed to
establish a connection, I would get the message "[x] is not answering" or
"...is not available... try again later" sort of thing, but then the program
would stop responding within 5-10 seconds. Similarly, when a call is ended by
a contact (either by directly hanging up or signing out/disconnecting from
WLM) I receive the message "[x] has ended the call" but then WLM freezes
within a few seconds. - If I end a call, it freezes immediately.
- If the call disconnects for some reason but both the contact and I remain
signed in on WLM, I do not receive a message stating the call has ended but
the other person will. (WLM doesn't freeze but if I was to choose to end the
call it would, so I just ctrl-alt-del the process and restart it.)

I'm at my wit's end with this frustrating problem. Previously I tried doing
a complete clean reinstall of WLM 8.5, and now WLM 9 Beta, without success.
What can be done? Any help is much appreciated.