Target failed to respond in time to a NOP request

Hi Experts,

I'm seeing the following errors appear on a Windows Server 2008 Ent R2 with an iSCSI connection to a QNAP NAS:

Event 48, BXOIS
Target failed to respond in time to a NOP request.

Event 20, BXOIS
Connection to the target was lost. The initiator will attempt to retry the connection.

Event 34, BXOIS
A connection to the target was lost, but Initiator successfully reconnected to the target. Dump data contains the target name.

These events occur within 2 seconds of each other, and appear almost every day, for large parts of the day.

I haven't had any reports of problems with this file share (the NAS is used to store general user/departmental data) so I'm not sure if it's causing a problem, but its really filling up the system logs and I'd like to figure out what the error means.

Thanks