More details are needed to determine the exact cause of the failure. For one, what switch is this, and what code is it running? Additionally, the ChangeAudit.log and JRun logs under NMSROOT\objects\jrun\jsm-cw2000\logs will be needed. Additional debugging may also need to be enabled.
Typical causes of vlan.dat fetch failures include a nonexistent vlan.dat (perhaps the switch is using a running-config based VLAN configuration), no telnet or SSH access to the switch (vlan.dat must be fetched using telnet or SSH and TFTP), or an issue with NAT between the device and the CiscoWorks server.
