More questions and suggestions:
Do you get any error messages?
Can you use a remote file share \\computer\sharename instead of a local
drive?
Can you verify with netmon that you are receiving packets and that you are
configured to log the packets you receive? (Auth, acct, and/or interim
acct?)
The log file probably won't be created until there is something to log...
Also, try checking out perfmon for IAS statistics. If you configure an RRAS
server to send acct-on messages, it won't start until the acct packet is
logged.
