When you compress a file using NTFS compression, Windows 2000 uses compression units, 16 clusters. If your cluster size is 4096 bytes, a compression unit is 65,536 bytes. This is the minimum calculated allocated space that is charged to a compressed file.
Disk quotas charges are based upon the calculated allocated space.
If you have 4K (4096 byte) clusters, a file of 158,208 bytes would allocate 39 clusters, 159744 bytes. If you compress the file, it will take 3 compression units, 196,608 bytes. This additional calculated allocation can cause you to exceed your disk quota limit.
The only workaround is to either decompress some files or to increase your disk quota limit.