NBU_VSP_Cache folder is getting Big and Big

I use the software: Symantec Netbackup 6.0 (formerly, Veritas Netbackup 6.0) on a Windows 2003 Server. The server has 3 disk partitions C:, D: and E:. A folder named NBU_VSP_Cache is created on all those partitions. The size of the folder is not the same on the different partitions. On C: Drive, it's 1.2 MB. On E: Drive, the folder is Empty. However, on the D: Drive it's bigger than 30 GB.

Because of that, the server is running out of space on the D: Drive.
My question is that: Is there any way to reduce the folder size, in order to save the disk space?