Event Log: The Exchange IFS failed to map drive ?

I have the following message in my Exchange Server computer's Application Log right after restarting the Exchange Server services:
"The Exchange IFS failed to map drive ?:. Please free drive ?: to use Exchange IFS."

I followed the link to Microsoft Article 273151 which says:
CAUSE
This behavior occurs because the Exchange IFS drive does not dynamically map. It gets mapped statically according to a registry value.

RESOLUTION
To resolve this behavior, change the mapping of the conflicting network drive.

Question: how can I find what drive letter the Exchange IFS drive is using via the Registry to I can map around it? Why do I have a question mark instead of a drive letter in the event log message?
LVL 4
GordonPrinceAsked:
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inbarasanCommented:
Dear GordonPrince,
> Exchange IFS failed to map drive
http://www.experts-exchange.com/Networking/Email_Groupware/Exchange_Server/Q_21521178.html
IFS drive is the M drive used in Exchange 2000. Make sure there are no mapped drive with the letter m:

http://support.microsoft.com/kb/305145/
Check the above article which says you can safely ignore the message

Cheers!
Inba

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