File Association problem in Win 2000

I need to associate a .syc file to a .exe file on a Win 2000 desktop. When I enter the file name in the 'open with' dialog and check the 'always use this program to open these files' it opens correctly. However, on subsequent attempts the association is gone. It works the first time only. In effect, the file association isn't happening. I have a second Win 200 machine where this works just fine. The machines are identical. Win 2000 is at build 2195. I appreciate any help.