Hi Justin, there are few things you could check, are the LUN's mounted for SME, SMSQL?
If you run a << snap list VOLNAME >> on the CLI for the appliance, do you see any snapshots listed? Always worth a check.
Has the LUN been dismounted and remounted at all?
By the looks of it you are using Snapdrive 6, have you tried to establish a new ISCSI session between the host and the Filer?
Are there any snapdrive entries in the windows event logs?
Is the issue isolated to 1 or 2 LUN's or all of them?
Checked the Username and Password for SnapDrive?