No Free/Busy Data Available When You Try to Schedule a Meeting

All of the sudden we had someone in our organization who's free/busy data would be grayed (or slashed) out when attempting to schedule a meeting with them. In an Exchange 2003 environment this user had roughly a 2GB mailbox so my thoughts were that the mailbox had gone beyond the point of no return. My first step was to archive the mailbox down to a reasonable size. Still no luck. What did the trick was running outlook from the run prompt by typing outlook.exe /cleanfreebusy