actually, the question was on c:\windows\csc folder. i know it's offline folder stuff there. but normally when you delete offline folders, the size of csc also reduces. but in this user's case, it didn't, until i deleted offline folder with ctrl+shift, which re-initialize offline folder cache.
this is what happened:
each user has their data folder in a server which is mapped to N:\ in their respective machine. their 'my documents' is targetted to this N:\ drive.
we also have shared folder in each server in branch offices which is mapped to S:\ in users machine.
most of laptop users make some folders in N:\ offline.
this user tried to make all data folder (N:\) AND shared folder (S:\) offline on his laptop and of course it was more than his HD capacity. after that, he noticed his HD was 99% full. option to undo "make available offline" was grayed out so he called me. i noticed that C:\Windows\CSC directory took most of the HD space and tried just deleting offline folders from Tools\Folder Options. It deleted the actual files but not in the CSC for some reasons. (i think it was bcuz it exceeded the HD capacity so it was never done "properly") then, i deleted offline folders with ctrl+shift. then, it recused the size of CSC but 'make available offline' is still grayed out. so i can't make them not available offline.
this is where i'm stuck at.