You can't disable its collection as it is an important file. However, in newer versions of LMS, you can disable the Change Audit record for this file under RME > Admin > Change Audit > Config Change Filter.
Note: by upgrading to LMS 2.6, you should have most of the vlan.dat related fixes which should hopefully fix this problem for you. Of course, vlan.dat is fetched in a unique way. In order to be able to fetch this file, RME will telnet or SSH to the switch in question, and then perform a "copy flash:vlan.dat tftp:". If you do not allow RME to connect to the switch interactively, this will, of course, fail.
For troubleshooting vlan.dat archival problems, I recommend a sniffer that captures all telnet and TFTP traffic from the CiscoWorks server to the switch (with SSH this is moot). As well as enabling ArchiveMgmt debugging under RME > Admin > System Preferences > Loglevel Settings, and looking at the dcmaservice.log for errors.
