Very strange. Enable logging on the switches (type logging buffered debug). When you experience a reload, look at the logs for some reason. Also if you type "show version" you get information on when and why the system was last reloaded.
Also upgrade the IOS to the latest version and see if it still happens. There is a known bug for malformed SNMP packets:
http://www.cisco.com/warp/public/707/cisco-malformed-snmp-msgs-pub.shtml
but I very much doubt that Ciscoworks would cause that!
Are you using dynamic VLANs by any chance (VMPS). I currently have a TAC case open regarding some instability with dynamic VLAN assignment on ports.
- Michael