Have you looked at the load balancer settings for the conversion service
?

1. It is not on a Domain controller, doc conversions won't work on
a DC

2. NetBIOS ports must be open between all servers in farm

3. All app pool idents are local admins on all servers in farm

4. It can resolve the ip address, by the netbios name, from the
command line

Sorry, I have to take issue with point 3. A basic security principle
of least privilege is that you avoid granting admin rights to
service accounts unless strictly necessary. Microsoft's
documentation is about service accounts for MOSS and their required
privileges is at http://technet2.microsoft.com/Office/en-
us/library/776589ed-aba4-47eb-8c4d-86905ac11a511033.mspx?mfr=true.

Having said that though, the statements in that document have
changed over time, and sometimes been self contradictory. And
although that document says that the installation process grants the
necessary privileges, at this stage of the product lifecycle that is
not true. A weather eye on the error log (watch for DCOM access
failures) and a healthy amount of auditing access failures are
needed to get the thing working!

I am merely repeating what the product team recommends - all app
pool identities are local admins.

I do not like this; in fact, I blogged about it in B2TR about my
disappointment in app pools being admins. But, yes, if you carefully set
DCOM security, this can be overcome. I obviously try not to send new
administrators into dcomcnfg.exe