incremental backup is almost as big as full backup

Hello,

i have a backup-job containing of a full backup at friday and incremental backups on monday to thursday. I tried the option incremtal with changed date and incremental using the archive bit. I make a full backup of a Windows 2008 Terminal Server. Most of the 40 GB are Windows and Programm files. There are also archived user-data on the server. So the data on this server actually hardly change but the size of the incremntal backups are almost as big as the size of the full backup (54 GB).

What could be the reason for that?

regards,

Joachim