In properties of the default email archive policy, click advanced, then get the pulldown marked desktop. Halfway down that large list will be the self install entry. Enable that. This will basically make your full clients in to lite clients. Click okay twice. Then go to the archiving task where the user is (per exch srvr), right click props, then click on the sync tab. Select sync, select users, and hit hte sync button. Choose'm out of a list and then hit okay.
Next test to see if the communications problem still exists. If it does, you know the problem isn't dcom. Most likely it's dns or routing (if comm is actually your problem, which I suspect it is). If it does work, DCOM is most likely your problem. In which case, just search this forum for DCOM hints (there's dozens).
Regardless, turn the self install feature back off, or your next sync will push that out to your entire environment.
micah