Large numbers of orphaned/expired requests

We are experiencing a situation where the SRS (2000 SP2) report server will no longer render reports. In the log file, there are many instances of

w3wp!runningjobs!434!3/23/2007-10:12:57:: i INFO: Adding: 8 running jobs to the database
w3wp!runningjobs!434!3/23/2007-10:13:57:: i INFO: RunningJobContext.IsClientConnected; found orphaned request
w3wp!runningjobs!434!3/23/2007-10:13:57:: i INFO: RunningJobContext.IsExpired; found expired request
w3wp!runningjobs!434!3/23/2007-10:13:57:: i INFO: RunningJobContext.IsExpired; found expired request
w3wp!runningjobs!434!3/23/2007-10:13:57:: i INFO: RunningJobContext.IsExpired; found expired request
w3wp!runningjobs!434!3/23/2007-10:13:57:: i INFO: RunningJobContext.IsClientConnected; found orphaned request
w3wp!runningjobs!434!3/23/2007-10:13:57:: i INFO: RunningJobContext.IsClientConnected; found orphaned request
w3wp!runningjobs!434!3/23/2007-10:13:57:: i INFO: RunningJobContext.IsExpired; found expired request
w3wp!runningjobs!434!3/23/2007-10:14:57:: i INFO: RunningJobContext.IsClientConnected; found orphaned request
w3wp!runningjobs!434!3/23/2007-10:14:57:: i INFO: RunningJobContext.IsExpired; found expired request
w3wp!runningjobs!434!3/23/2007-10:14:57:: i INFO: RunningJobContext.IsExpired; found expired request
w3wp!runningjobs!434!3/23/2007-10:14:57:: i INFO: RunningJobContext.IsExpired; found expired request
w3wp!runningjobs!434!3/23/2007-10:14:57:: i INFO: RunningJobContext.IsClientConnected; found orphaned request
w3wp!runningjobs!434!3/23/2007-10:14:57:: i INFO: RunningJobContext.IsClientConnected; found orphaned request
w3wp!runningjobs!434!3/23/2007-10:14:57:: i INFO: RunningJobContext.IsExpired; found expired request

What could be causing this? The reports are making queries through an OLE DB provider. There are no scheduled jobs, and the load doesn't seem that heavy.
Orphaned request indicates that the HTTP request has gone away before we finished processing the report. Generally this is because people request a report, and then close IE.